Move fixtures from test-requirments to requirments

Fixtures are required by oslo.lockutils so we should move them to
requirments.

And could move it back after this patch
https://review.openstack.org/#/c/52612/
Will be merged

Change-Id: I018a603c994cf8573020cca28b77fa5716038d8e
Closes-bug: #1241581