[Fix gate]Update test requirement
[Fix gate]Update test requirement

Since pbr already landed and the old version of hacking seems not
work very well with pbr>=2, we should update it to match global
requirement.
Partial-Bug: #1668848

Change-Id: I1ee774a4bccc58e9d10b5525e919f1b6f3d40b3b

openstack/congress,openstack/congress