Use class FakeServer in TestServerImageCreate.
Use class FakeServer in TestServerImageCreate.

There are the same problems with TestServerCreate in TestServerImageCreate.
Use the new class FakeServer to fix them.

Change-Id: Ie723fa95620549f09a81ef72953f46877ef9252a
Implements: blueprint osc-unit-test-framework-improvement

BjoernT/python-openstackclient,redhat-openstack/python-openstackclient,openstack/python-openstackclient,redhat-openstack/python-openstackclient,openstack/python-openstackclient,dtroyer/python-openstackclient,dtroyer/python-openstackclient,BjoernT/python-openstackclient