[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: Id99d96e249ab285dddf0a88706c5bca9f0ea3a6d

openstack/solum,stackforge/solum,stackforge/solum,openstack/solum