initialize ctx.manager in ceph.py

initialize ctx.manager in ceph.py

instead of rados.py because ceph.py is only run once where rados.py
could be run multiple time, leading to race conditions

http://tracker.ceph.com/issues/9027 Fixes: #9027

Signed-off-by: Loic Dachary <loic@dachary.org>
(cherry picked from commit 9782465c872b25710af278c701e15078a3748d03)

Conflicts:
	tasks/rados.py
        because  if not hasattr(ctx, 'manager'): was not at the same place