Add support for glusterfs native protocol driver

This patch adds basic support for glusterfs native protocol driver
that uses cert based access type.

A Manila share is a GlusterFS volume. Unlike the generic driver, this
does not use service VM approach. Instances directly talk with the
GlusterFS backend storage pool. Instance use the 'glusterfs' protocol
to mount the GlusterFS share. Access to the share is allowed via
SSL Certificates. Only the share which has the SSL trust established
with the GlusterFS backend can mount and hence use the share.

Establishing the SSL trust between the instance and backend is done
out of band of Manila.

Partially-implements blueprint cert-based-access-type

Change-Id: I229d481086478317f1c43635304a16794372f09d
Merge "Add support for glusterfs native protocol driver"