qa: scripts to help test ceph-qa-suite

This workunit will be used by tests as a placeholder that always return
true. This is helpful in tests when a script from the qa/workunits
directory is mandatory but we do not care about testing anything.  For
an example of how it can be used, check
https://github.com/ceph/ceph-qa-suite/pull/120

Signed-off-by: Loic Dachary <loic-201408@dachary.org>