Add fixtures into test-requirements
Add fixtures into test-requirements

We have broken gate, because we have no limitation to fixtures,
and the new version is incompatible to us.
We need to add fixtures into test-requirements to make
sure that we always up to date with global requirements.
Closes-Bug: #1567731

Change-Id: Ib0cac0c217db195ce3723cee3f09d26e6be9f0ea

cwolferh/heat-scratch,noironetworks/heat,noironetworks/heat,openstack/heat,openstack/heat,steveb/heat,cwolferh/heat-scratch,steveb/heat