Adjust version constraint of hacking

Neutron constrained the version of hacking < 1.2.0, but since then the
unit tests fails with:

ERROR: Double requirement given: hacking<1.2.0,>=1.1.0 (from -ri https://opendev.org/openstack/neutron/raw/branch/master/test-requirements.txt (line 4)) (already in hacking>=1.1.0 (from -r [..]networking-powervm/test-requirements.txt (line 4)), name='hacking')

So let's simply use the same constraint as set in neutron.

Change-Id: Ic4d97db6c947264806e5ef9e35f21f764cbecf46

test-requirements.txt

@@ -1,7 +1,7 @@
 # The order of packages is significant, because pip processes them in the order
 # of appearance. Changing the order has an impact on the overall integration
 # process, which may cause wedges in the gate later.
-hacking>=1.1.0 # Apache-2.0
+hacking>=1.1.0,<1.2.0 # Apache-2.0
 bashate>=0.5.1 # Apache-2.0
 coverage!=4.4,>=4.0 # Apache-2.0
 fixtures>=3.0.0 # Apache-2.0/BSD