…ssions' rule

Fixes: ComplianceAsCode#834

Testing report:
---------------
The proposed change has been tested manually on recent RHEL-7 system &
AFAICT from testing it's working fine.

Note:
-----
This remediation script will NOT put the system in question into 'fixed'
state. This is because even after performing the remediation (calling
permissions that saved in the RPM database there will remain one unfixed
file path, namely "/var/log/gdm". The issue here being that this is known
bug:
  [1] https://bugzilla.redhat.com/show_bug.cgi?id=1277603

reported to downstream bugzilla (till calling "# rpm --setperms gdm"
won't fix the problem also for the "/var/log/gdm" location, the returned
result of this remediation script will be 'error' instead of 'fixed').

But the proper work of this remediation can be verified by running the command:

before and after the remediation and comparing the results (the count of
files reported before the remediation will be higher than count of files
having incorrect permissions after the remediation has finished -- the
only unfixed exception should be "/var/log/gdm" file path and we have
bugs reported downstream for these).

  ComplianceAsCode#879 (comment)

add a <warning> into the RHEL-6 & RHEL-7 XCCDF prose for 'rpm_verify_permissions'
rule explaining that (due to RHEL-6 & RHEL-7 gdm package bugs) the corresponding
OVAL may still fail after performing remediation due to permissions on /var/log/gdm
location still not to be configure properly. Also provide links to corresponding
RHEL-6 and RHEL-7 Red Hat Bugzilla reports.