Only ask RHEL specific questions when run on RHEL

Putting the RHEL specific questions into a separate group and
adding a is_rhel pre-condition so non-RHEL users won't get bugged
in interactive mode.

Also, one of the tests will no longer make sense on non-RHEL
platforms and has therefore been disarmed on those. Since all tests
are always also run on RHEL, this should be of no concern.

Change-Id: I7f39762dd9ad60545bff993ec99c8e4acfe10e2e
Fixes: https://bugzilla.redhat.com/show_bug.cgi?id=921545
Merge "Only ask RHEL specific questions when run on RHEL"