Update test requirement
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: I118969b4b3e8e94672a207432600f65aa38131a9

openstack/freezer-web-ui,openstack/freezer-web-ui,openstack/freezer-web-ui,openstack/freezer-web-ui