Remove ansible managed header from ceph.conf

In ceph-common you load {{ ansible_managed }} at the top of the main
config file - this will trigger handlers on that file whenever an
Ansible run is made.

I'd suggest replacing it with a vanilla text comment 'managed by
Ansible' to warn
admins but avoid unnecessary cluster bounces.

fixes: #125

Signed-off-by: Sébastien Han <sebastien.han@enovance.com>