vfs_ceph_new: Add a new struct to hold ceph module config

vfs_ceph_new: Add a new struct to hold ceph module config

Consolidate all required configuration related data under a dedicated
structure named vfs_ceph_config. As of now it includes the location of
configuration file, file system name, ceph client user id and mount
related information. This is expected to grow in future with more
details as and when required. Apart from that small cleanups are also
done to make code more robust.

BUG: https://bugzilla.samba.org/show_bug.cgi?id=15703

Pair-Programmed-With: Anoop C S <anoopcs@samba.org>
Signed-off-by: Guenther Deschner <gd@samba.org>
Signed-off-by: Anoop C S <anoopcs@samba.org>
Reviewed-by: Guenther Deschner <gd@samba.org>