Clean Up EMC VNX Direct Driver in Cinder

This patch cleans up issues discovered during the review of
EMC VNX Direct Driver.

https://review.openstack.org/#/c/73672/

Implements blueprint emc-vnx-direct-driver
Closes-Bug: #1287944

Change-Id: I4002ef9ea14e2d843dd8cbccffa025997a54c738
Merge "Clean Up EMC VNX Direct Driver in Cinder"