Remove glusterfs_disk_util option

The glusterfs_disk_util option has been removed. I have manually
removed this entry from the current configuration tables and the
flag mapping.

As it is no longer in the code it will also no longer appear in
future auto-generated versions of the tables.

Closes-Bug: #1259419

Change-Id: I4aa606b3920347caa896c5b65ddcff6d9faf9881
Added Complete Doc conventions to user-guide-admin.

Change-Id: I1c9a4d1a20a0dacf88fab705a0226ed1f7a39a8f
Closes-Bug: #1121866
Merge "Added Complete Doc conventions to user-guide-admin."
Merge "Remove glusterfs_disk_util option"