Introduce FakeVolume class
Introduce FakeVolume class

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

Change-Id: I9d56efa4fd4f03c82cd4e29622b6312566dbc453
Implements: blueprint improve-volume-unittest-framework

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