Remove mox in helpers.py
Remove mox in helpers.py

Replace mox with mock in helpers.py

Change-Id: I277ecce0a2b1af0cbd0f1cd06403c2f318e254a4
Partially-Implements: blueprint remove-mox-ocata

openstack/magnum-ui,openstack/magnum-ui,openstack/magnum-ui,openstack/magnum-ui