Fix Devstack and Manila-ui interaction
Fix Devstack and Manila-ui interaction

Devstack always installs test-requirements, but we do not expect it for
Manila UI project. Moreover, such installation started failing with
PIP versions 8.x
Change that triggered bug is Devstack change at [1].

[1] I49658ce4056c773943321270defd461bbf3e9fb9

Change-Id: I841b56f65b50e9c5673cc02e93b4329ed29125ba
Closes-Bug: #1540188

NetApp/manila,vponomaryov/manila,openstack/manila,bswartz/manila,NetApp/manila,openstack/manila,vponomaryov/manila,bswartz/manila