qa/tasks/ceph_manager.py: dump more useful info before failing

qa/tasks/ceph_manager.py: dump more useful info before failing

Add helpers that dump information only about PGs that haven't reached
the desired state when we fail. Previously we dumped the output of
"ceph pg dump" before failing, which prints a lot of unnecessary information
about PGs that are not responsible for the failure, making debugging harder.

Also, try to make the failure messages distinct.

Signed-off-by: Neha Ojha <nojha@redhat.com>