qa/cephfs: allow finer control on test runs

qa/cephfs: allow finer control on test runs

When working with large group tests (18 in this case), it gets very
tedious to debug and fix tests when all 18 have to be run again for
every mistake. Cheap fix for this to split these 18 tests into several
classes.

But when modification are made to the feature, all these 18 tests needs
to exercised and previous solution forces developer to intitiate all
these test classes to run one by one.

Best of both worlds can be achieved if we split tests into group but
move all these related group to a new file.

Signed-off-by: Rishabh Dave <ridave@redhat.com>
(cherry picked from commit 9c547ad2a570a325ea453ccc9419be2b8bc06b28)