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
Gracefully handle Users with no email attribute

In certain environments, such as when using Keystone with a LDAP
backend, it's possible that the email attribute won't exist for all
users.

Change-Id: I71041be832206e52bfb73926199f2c89e0e84a0b
Closes-Bug: #1260423
Merge "Adds Cinder client mock to tests"
Merge "Gracefully handle Users with no email attribute"