First version of Cinder driver for Quobyte USP

First version of Cinder driver for Quobyte USP

Supported Operations are:
- Create Volume
- Delete Volume
- Attach Volume
- Detach Volume
- Extend Volume
- Create Snapshot
- Delete Snapshot
- List Snapshots
- Create Volume from Snapshot
- Create Volume from Image
- Create Volume from Volume (Clone)
- Create Image from Volume

The driver uses a file-based interface to access the configured
Quobyte volume. Therefore, the driver is similar to the existing
drivers NFS and GlusterFS.

Due to the similarities, I reused the snapshot code from the GlusterFS
driver. Gluster, thanks for that! I've kept the "Red Hat" copyright in
the header to credit you properly.

All driver functions are covered by unit tests. Snapshot tests were
taken over from test_glusterfs.py. New tests are written using "Mock"
instead of "mox".

Certification tests: https://bugs.launchpad.net/cinder/+bug/1401471

Implements: blueprint quobyte-usp-driver
Change-Id: I7ca13e28b000d7a07c2baecd5454e50be4c9640b