Replaces mox with mock in api's unit tests

OpenStack is moving unit tests from mox to mock for python3.3 compatibility.
This replaces mox with mock in api's unit tests.

It also fixes a slight problem with ..test_nodes.TestPut.test_power_state_in_progress().
mox was generating the exception (due to a second call to .update_node()), not
the ironic code. This is because objects.Node.get_by_uuid() returns a different
node (that gets its state changed) and the original node never gets the change.
When it is mocked to return the same node, the expected exception is raised by
ironic.api.controllers.v1.node.NodePowerStateController.put().

Change-Id: If734fb4c9a4a386ccc37a1336dbd41e3121a5ef4
Merge "Replaces mox with mock in api's unit tests"