Bring EMC VNX support for volumes backend

- Add a new backend to support EMC VNX direct driver
- Updating puppet-cinder refs to have the upstream commit with EMC
  support
- Unit test with a new context
- Update the README

Note: .fixtures and Puppetfile has been put on a dev branchi for cinder module to debug while the patch is upstream.
Merge pull request #640 from enovance/emc_vnx

Bring EMC VNX support for volumes backend