Add RBD test for volume not existing during delete

For cases when the volume does not exist in the backend, but Cinder
still knows about it, we just return from the rbd driver and let Cinder
do its thing.

Change-Id: I6150756bdd48259ec8d550fa7a5dc7a9f882ca22
Merge "Add RBD test for volume not existing during delete"
(Test commit) Change README to reflect Jio's fork of Cinder

Change-Id: I3f26c0a736e63725aec24ca2fa12c707b8e6460f