tests: temporarily limit max version of prospector

* Due to landscapeio/prospector#335 the latest
  version of prospector fails to run pylint. Forcing the max version of
  it to the last one that runs without errors temporarily.

Change-Id: I7b924e32a7c3110943ceb52f8bddf0d1dace2ce9

setup.py

@@ -13,7 +13,7 @@
     'tests': [
         'bandit>=1.1.0',
         'flake8>=3.2.1',
-        'prospector[with_everything]>=0.12.4',
+        'prospector[with_everything]>=0.12.4,<=1.1.6.2',
     ],
 }