Catch correct exception for Cinder api version detection

Catch the EndpointNotFound exception raised by Keystone rather
than the one thrown by Cinder since keystoneclient raises keystone
exceptions and not cinder exceptions. Also update the fake
keystone client to mirror this behavior.

Change-Id: I9f4579cf55fc697470dd8803553d7968e22a6bec
Closes-Bug: #1382659
Merge "Catch correct exception for Cinder api version detection"