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:
# of appearance. Changing the order has an impact on the overall integration
# process, which may cause wedges in the gate later.
# Metrics and style
-hacking<0.11,>=0.10.0
+hacking>=0.12.0,!=0.13.0,<0.14 # Apache-2.0
# Packaging
mock>=2.0 # BSD
