[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.

Change-Id: I4aeb9a67344c2566545219d079032af0ceb510b4
Partial-Bug: #1668848

stackforge/cloudkitty-dashboard,stackforge/cloudkitty-dashboard,openstack/cloudkitty-dashboard,openstack/cloudkitty-dashboard,openstack/cloudkitty-dashboard,stackforge/cloudkitty-dashboard