Introduce FakeImage class
Introduce FakeImage class

Introduce FakeImage to improve the current image unittest framework
with following two advantages:
1. generate more than one faking images
2. all faking images generated by random

Change-Id: Ide326fa2a047ddeea478bef97000083617a0b744
Implements: blueprint improve-image-unittest-framework

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