Adds Cinder client mock to tests

Test cases now have a mock for the method tenant_absolute_limits
in cinder client. The absence of this mock was causing real HTTP
requests from this client.

Change-Id: I8b9c4f5affc43e2649f3ebf08580bb3d3687e09b
Closes-Bug: #1259533
Merge "Adds Cinder client mock to tests"