Add NFS/GlusterFS support to brick library

Refactor NFS driver to use the brick library to perform mounts
rather than duplicating the mount code. Some of the NFS unit
test code was rewritten to test the brick implementation because
the old mount code was moved.

The Gluster driver was slightly affected in the refactoring, but
does not yet use brick to perform attaches.

bug 1214748

Change-Id: Ib29f83fabe407f9591191e9fd19e6306ca9960cf
Add kwargs to create_volume in tests/utils.py

Add availability_zone parameter and kwargs to make create_volume
function more flexible in order to use this function in
unit tests.
The goal is to remove inner _create_volume function in:
- db/test_transfers.py
- api/contrib/test_backups.py
- test_gpfs.py
- test_volume_transfer.py
- test_volume.py
and to use create_volume from tests/utils instead.

Change-Id: I2d9456ff3ff1cd945042f19c47e40f9f0ec0fe8a
Merge "Add NFS/GlusterFS support to brick library"
Merge "Add kwargs to create_volume in tests/utils.py"