Move python-tackerclient to new hacking 4.0.0

New rule enforcement has been enabled in the latest hacking code.

This patch bumps new version of hacking in test-requirements file,
for early detection and to avoid code breakage later when hacking
changes are released.

Change-Id: Ic54af7096b58259d6ee434a743ce9b75b7b61f28

test-requirements.txt

@@ -2,7 +2,7 @@
 # of appearance. Changing the order has an impact on the overall integration
 # process, which may cause wedges in the gate later.
 
-hacking>=3.0.1,<3.1.0 # Apache-2.0
+hacking>=4.0.0,<4.1.0 # Apache-2.0
 coverage!=4.4,>=4.0 # Apache-2.0
 ddt>=1.0.1 # MIT
 fixtures>=3.0.0 # Apache-2.0/BSD