ceph: use wait_for_clean before scrub

Signed-off-by: Samuel Just <sam.just@inktank.com>
ceph: verify that snaps were trimmed

Signed-off-by: Samuel Just <sam.just@inktank.com>
rados: don't clean up pools, we want to scrub them!

Signed-off-by: Samuel Just <sam.just@inktank.com>
Merge remote-tracking branches 'origin/wip-sam-misc' and 'origin/wip-snaps' into wip-sam-testing