move functions from ceph to ceph_manager

mount_osd_data and make_admin_daemon_dir are only used by
ceph_manager.py although they are defined in ceph.py

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