Add unit tests for compute v2 aggregate
Add unit tests for compute v2 aggregate

This patch add the complete unit tests to cover compute v2
aggregate object.

Change-Id: Ifcf9248eabb5ca3ee5ca01c5843e96ba681c3b5a
Closes-Bug: #1560832

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