[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: I8126567017aaa3fcc8bd842abe318690bdcb1110

openstack/python-searchlightclient,openstack/python-searchlightclient