* Create file-check functionality into utility file
There are the similar issues as PR #2302. Almost resources return false
positives when a file does not exist or is not read.
* Replace to file-check functionality
* Fix dh_params and x509_certificate resources
If a file is empty, OpenSSL::PKey::DH and OpenSSL::X509::Certificate have
raised an exception and have skipped the inspection. Thus x509_certificate
and dh_params resources are not allowed to read a empty file.
* to_s of shadow expects filters is not nil
* Remove workaround of sshd_config
Removes the workaround of sshd_config since Travis CI fails due to a bug
of dev-sec/ssh-baseline and the PR #100 will fix it.
* Use init block variable in methods
Signed-off-by: ERAMOTO Masaya <eramoto.masaya@jp.fujitsu.com>