qa/cephfs: add 'rhel' to family of RH OS in xfstest_dev.py

qa/cephfs: add 'rhel' to family of RH OS in xfstest_dev.py

The string returned by get_system_type() for RHEL 8.4 recently wasn't
one of the strings that xfstests_dev.py expects. The string returned
this time was instead "rhel". Add this string to the list of strings
that xfstests_dev.py expects for Red Hat OS family so that this failure
won't occur again in future. Also log the detected distro and version so
that it is easier to debug when this issue occurs next time.

Fixes: https://tracker.ceph.com/issues/58726
Signed-off-by: Rishabh Dave <ridave@redhat.com>