Implement extend volume functionality in Sheepdog

This implements the extend volume functionality for Sheepdog driver.

Change-Id: Id7361e9571742bea210f13ced722829f489e7cb0
Implements: blueprint extend-sheepdog-volume
CoraidDriver: Allow volumes in error state to be deleted

This fix will allow the delete call to be successfull if volume
doesn't exists on the SAN.

Fixes bug 1195788

Change-Id: I0396f1252c8faafff3e8b4f9a4aeffb930350a8d
Merge "CoraidDriver: Allow volumes in error state to be deleted"