tests: Moving sleep call after action in ceph_watch_wait()

tests: Moving sleep call after action in ceph_watch_wait()

ceph_watch_wait() is doing a sleep _before_ doing the test which could
stop this loop.

It's better doing the action first as it could exit immediately and
avoid a useless sleep.

That's a minor optimization but everything count when trying to get
something smooth.

Signed-off-by: Erwan Velu <erwan@redhat.com>