add "packages" resource

This pull request adds a packages resource so that we can check for pattern matches against all the packages on a system. This initially implements only dpkg support for debian-based platforms so we can cover this use case:

```ruby
describe packages(/^xserver-xorg.*/) do
  its("list") { should be_empty }
end
```

This uses FilterTable so we can supply additional queries, too.

```ruby
describe packages(/vi.+/).where { status != 'installed' } do
  its('statuses') { should be_empty }
end
```

Users can specify the name as a string or a regular expression. If it is a string, we will escape it and convert it to a regular expression to use in matching against the full returned list of packages. If it is a regular expression, we take that as is and use it to filter the results.

While some package management systems such as `dpkg` can take a shell glob argument to filter their results, we eschew this and require a regular expression to match multiple package names because we will need this to work across other platforms in the future. This means that the following:

```ruby
packages("vim")
```

Will return *all* the "vim" packages on the system. The `packages` resource will take `"vim"`, turn it into `/vim/`, and greedily match anything with "vim" in the name. To match only a single package named `vim`, it needs to be an anchored regular expression.

```ruby
packages(/^vim$/)
```

Signed-off-by: Joshua Timberman <joshua@chef.io>

Use entries instead of list

Added a few more tests and non installed package in output
Signed-off-by: Alex Pop <apop@chef.io>

fix lint

Signed-off-by: Alex Pop <apop@chef.io>

Signed-off-by: Joshua Timberman <joshua@chef.io>

lib/inspec/resource.rb

@@ -107,6 +107,7 @@ require 'resources/oneget'
 require 'resources/os'
 require 'resources/os_env'
 require 'resources/package'
+require 'resources/packages'
 require 'resources/parse_config'
 require 'resources/passwd'
 require 'resources/pip'

lib/resources/packages.rb

@@ -0,0 +1,86 @@
+# encoding: utf-8
+# copyright: 2017, Chef Software, Inc. <legal@chef.io>
+# author: Joshua Timberman
+# author: Alex Pop
+# license: All rights reserved
+
+require 'utils/filter'
+
+module Inspec::Resources
+  class Packages < Inspec.resource(1)
+    name 'packages'
+    desc 'Use the packages InSpec audit resource to test properties for multiple packages installed on the system'
+    example "
+      describe packages(/xserver-xorg.*/) do
+        its('entries') { should be_empty }
+      end
+      describe packages('vim').entries.length do
+        it { should be > 1 }
+      end
+      describe packages(/vi.+/).where { status != 'installed' } do
+        its('statuses') { should be_empty }
+      end
+    "
+
+    def initialize(pattern)
+      @pattern = pattern_regexp(pattern)
+      all_pkgs = package_list
+      @list = all_pkgs.find_all do |hm|
+        hm[:name] =~ pattern_regexp(pattern)
+      end
+    end
+
+    def to_s
+      "Packages #{@pattern.class == String ? @pattern : @pattern.inspect}"
+    end
+
+    filter = FilterTable.create
+    filter.add_accessor(:where)
+          .add_accessor(:entries)
+          .add(:statuses,  field: 'status', style: :simple)
+          .add(:names,     field: 'name')
+          .add(:versions,  field: 'version')
+          .connect(self, :filtered_packages)
+
+    private
+
+    def pattern_regexp(p)
+      if p.class == String
+        Regexp.new(Regexp.escape(p))
+      elsif p.class == Regexp
+        p
+      else
+        fail 'invalid name argument to packages resource, please use a "string" or /regexp/'
+      end
+    end
+
+    def filtered_packages
+      @list
+    end
+
+    def package_list
+      os = inspec.os
+
+      if os.debian?
+        command = "dpkg-query -W -f='${db:Status-Abbrev} ${Package} ${Version}\\n'"
+      else
+        fail "packages resource is not yet supported on #{os.name}"
+      end
+      build_package_list(command)
+    end
+
+    Package = Struct.new(:status, :name, :version)
+
+    def build_package_list(command)
+      cmd = inspec.command(command)
+      all = cmd.stdout.split("\n")[1..-1]
+      return [] if all.nil?
+      all.map do |m|
+        a = m.split
+        a[0] = 'installed' if a[0] =~ /^.i/
+        a[2] = a[2].split(':').last
+        Package.new(*a)
+      end
+    end
+  end
+end

test/helper.rb

@@ -50,6 +50,7 @@ class MockLoader
     ubuntu1204: { name: 'ubuntu', family: 'debian', release: '12.04', arch: 'x86_64' },
     ubuntu1404: { name: 'ubuntu', family: 'debian', release: '14.04', arch: 'x86_64' },
     ubuntu1504: { name: 'ubuntu', family: 'debian', release: '15.04', arch: 'x86_64' },
+    ubuntu1604: { name: 'ubuntu', family: 'debian', release: '16.04', arch: 'x86_64' },
     mint17:     { name: 'linuxmint', family: 'debian', release: '17.3', arch: 'x86_64' },
     mint18:     { name: 'linuxmint', family: 'debian', release: '18', arch: 'x86_64' },
     windows:    { name: 'windows', family: 'windows', release: '6.2.9200', arch: 'x86_64' },
@@ -249,6 +250,8 @@ class MockLoader
       'pkginfo -l SUNWzfsr' => cmd.call('pkginfo-l-SUNWzfsr'),
       # solaris 11 package manager
       'pkg info system/file-system/zfs' => cmd.call('pkg-info-system-file-system-zfs'),
+      # dpkg-query package list
+      "dpkg-query -W -f='${db:Status-Abbrev} ${Package} ${Version}\\n'" => cmd.call('dpkg-query-W'),
       # port netstat on solaris 10 & 11
       'netstat -an -f inet -f inet6' => cmd.call('s11-netstat-an-finet-finet6'),
       # xinetd configuration

test/unit/mock/cmd/dpkg-query-W

@@ -0,0 +1,12 @@
+ii  bash 4.3-14ubuntu1.1
+rc  fakeroot 1.20.2-1ubuntu1
+rc  libfakeroot 1.20.2-1ubuntu1
+ii  overlayroot 0.27ubuntu1.2
+ii  vim 2:7.4.1689-3ubuntu1.2
+ii  vim-common 2:7.4.1689-3ubuntu1.2
+ii  xorg 1:7.7+13ubuntu3
+ii  xorg-docs-core 1:1.7.1-1ubuntu1
+ii  xserver-common 2:1.18.4-0ubuntu0.2
+ii  xserver-xorg 1:7.7+13ubuntu3
+ii  xserver-xorg-core 2:1.18.4-0ubuntu0.2
+ii  xserver-xorg-input-all 1:7.7+13ubuntu3

test/unit/resources/packages_test.rb

@@ -0,0 +1,59 @@
+# encoding: utf-8
+# author: Joshua Timberman
+
+require 'helper'
+require 'inspec/resource'
+
+describe 'Inspec::Resources::Packages' do
+  it 'verify packages resource' do
+    resource = MockLoader.new(:ubuntu1604).load_resource('packages', /^vim$/)
+    _(resource.entries.length).must_equal 1
+    _(resource.entries[0].to_h).must_equal({
+      status: 'installed',
+      name: 'vim',
+      version: '7.4.1689-3ubuntu1.2',
+    })
+  end
+
+  it 'package name matches with output (string)' do
+    resource = MockLoader.new(:ubuntu1604).load_resource('packages', 'xserver-xorg')
+    _(resource.to_s).must_equal 'Packages /xserver\\-xorg/'
+  end
+
+  it 'packages using where filters' do
+    resource = MockLoader.new(:ubuntu1604).load_resource('packages', /.+root$/)
+    _(resource.entries.length).must_equal 3
+    _(resource.where { status != 'installed' }.names).must_equal(['fakeroot', 'libfakeroot'])
+    _(resource.where { version =~ /^0\.2.+/ }.entries[0].to_h).must_equal({
+      status: "installed",
+      name: "overlayroot",
+      version: "0.27ubuntu1.2",
+    })
+  end
+
+  it 'package name matches with output (regex)' do
+    resource = MockLoader.new(:ubuntu1604).load_resource('packages', /vim/)
+    _(resource.to_s).must_equal 'Packages /vim/'
+  end
+
+  it 'returns a list of packages with a wildcard' do
+    resource = MockLoader.new(:ubuntu1604).load_resource('packages', /^xserver-xorg.*/)
+    _(resource.statuses).must_equal ['installed']
+    _(resource.entries.length).must_equal 3
+  end
+
+
+  it 'fails on non debian platforms' do
+    proc {
+      resource = MockLoader.new(:centos6).load_resource('packages', 'bash')
+      resource.send(:entries, nil)
+    }.must_raise(RuntimeError)
+  end
+
+  it 'fails if the packages name is not a string or regexp' do
+    proc {
+      resources = MockLoader.new(:ubuntu1604).load_resource('packages', [:a, :b])
+      resources.send(:entries, nil)
+    }.must_raise(RuntimeError)
+  end
+end