convert test_domain to use requests_mock
convert test_domain to use requests_mock

convert all of the test_domain cases to use requests_mock.

Change-Id: I3f24eaaab236c136690d3314b242c1e6ae5b6720

openstack-infra/shade,dtroyer/python-openstacksdk,openstack/python-openstacksdk,stackforge/python-openstacksdk,stackforge/python-openstacksdk,openstack-infra/shade,dtroyer/python-openstacksdk,openstack/python-openstacksdk