Trivial: Fix wrong comment in test_image.py
Trivial: Fix wrong comment in test_image.py

Code in test_image.py has nothing to do with server.

Change-Id: Ia73d7b99effb394c5db9635fee6da350b0b1086b

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