doc: Added separate troubleshooting for MDS and Ceph FS.

Signed-off-by: John Wilkins <john.wilkins@inktank.com>
doc: Added troubleshooting to Ceph FS index.

Signed-off-by: John Wilkins <john.wilkins@inktank.com>
doc: Updated Ceph FS Quick Start.

Signed-off-by: John Wilkins <john.wilkins@inktank.com>