Fix description errors in volume fakes
Fix description errors in volume fakes

In volumev2 fakes.py. Description of some 'get_*' methods is incorrect.
the error will mislead the user. this patch has already fixed it.

Change-Id: I048e3c2b625c7b54ab19f2b923d4970427f277ff

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