Don't install package dependencies for flake8

Use hacking==0.7.

Change-Id: I53dc938efef39ba7bd82deec6bc8bb2e48466530

tox.ini

@@ -15,6 +15,7 @@ commands =
 downloadcache = ~/cache/pip
 
 [testenv:pep8]
+deps = hacking==0.7
 usedevelop = False
 commands =
     flake8 {posargs:fuelclient}