Add GlusterFS protocol as a supported Share/NAS type

This patch adds GlusterFS as a supported protocol (in addition
to NFS and CIFS) in the Share/NAS type doc/help string. Since the
Manila server side now support cert based access type which
introduced 'glusterfs' as a new share protocol, this patch
updates the manilaclient help/doc string to reflect the same.

'glusterfs' protocol support was added to server side using:
https://review.openstack.org/116859

Change-Id: I94cbecd55fabbfd1bb7c06184e4679c7531d0214
Closes-Bug: #1367205