Save off supports[:os] and restore it after each test.

This fixes some other tests that require supports[:os] to be correct.

Signed-off-by: Ryan Davis <zenspider@chef.io>

test/unit/plugin/v1/resource_test.rb

@@ -57,10 +57,15 @@ describe Inspec::Plugins::Resource do
 
   describe "supported platform" do
     def supports_meta(supports)
+      @old = Inspec::Resource.supports[:os]
       Inspec::Resource.supports[:os] = supports
       load_resource("os")
     end
 
+    after do
+      Inspec::Resource.supports[:os] = @old
+    end
+
     it "loads a profile which supports multiple families" do
       m = supports_meta([
         { os_family: "windows" },