Replace mox3 with mock

In heat, some unit tests still use mox3,
which will make the test speed much slow, so I decide to remove it.
Next, i will modify the next files:

(1)contrib/rackspace/heat_keystoneclient_v2/tests/test_client.py
(2)contrib/rackspace/rackspace/tests/test_cloud_loadbalancer.py
(3)heat/tests/aws/test_eip.py
(4)heat/tests/aws/test_instance.py
(5)heat/tests/aws/test_volume.py
(6)heat/tests/clients/test_heat_client.py
(7)heat/tests/common.py
(8)heat/tests/db/test_sqlalchemy_api.py
(9)heat/tests/engine/tools.py
(10)heat/tests/openstack/aodh/test_alarm.py
(11)heat/tests/openstack/aodh/test_gnocchi_alarm.py
(12)heat/tests/openstack/heat/test_waitcondition.py
(13)heat/tests/openstack/neutron/test_neutron_floating_ip.py
(14)heat/tests/openstack/neutron/test_neutron_net.py
(15)heat/tests/openstack/neutron/test_neutron_port.py
(16)heat/tests/openstack/neutron/test_neutron_router.py
(17)heat/tests/openstack/neutron/test_neutron_security_group.py
(18)heat/tests/openstack/neutron/test_neutron_vpnservice.py
(19)heat/tests/test_auth_password.py
(20)heat/tests/test_engine_service.py
(21)heat/tests/test_stack.py
(22)heat/tests/test_stack_update.py
(23)heat/tests/utils.py
(24)heat/tests/generic_resource.py
(25)heat/tests/openstack/neutron/test_neutron_loadbalancer.py