Offline snapshots for GlusterFS volumes

Offline snapshots for the GlusterFS driver, based
on QCOW2 snapshotting.

This also introduces the option to have volumes stored
as qcow2 files rather than raw files.

Bump driver version to 1.1.

Online snapshot support (via Nova) is added in a
subsequent patch submitted in this series.

Implements blueprint qemu-assisted-snapshots
DocImpact

Change-Id: I783a802574b835b495e343f555f7ecf9b46981dd
Offline snap Tests
Allow Cinder to call Nova client

This code allows Cinder to call Nova client functions. This will be used
for online migration and guest-assisted snapshots, which are both in
progress.

Change-Id: I9c94917bddcf250b880ca730df463a8402fe6b1d
Enable access to Nova admin API endpoint

Note: includes compute/__init__.py from Avishay's
https://review.openstack.org/#/c/41285/

This will be merged outside of this patch.
Guest-assisted-snapshots for GlusterFS volumes

Coordinate with Nova to create and delete snaphots online for
GlusterFS volumes.

Cinder is responsible for creating a qcow2 file which Nova
will activate in the VM's snapshot chain.

Implements blueprint qemu-assisted-snapshots

Conflicts:
	cinder/volume/drivers/glusterfs.py
Extend volume for GlusterFS

Add support for extend volume

Submit as separate gerrit review