[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: Ifc80e70434d99ab04d12a744e66daa2fea8ebe4b

openstack/barbican,openstack/barbican