Adds initial hacking checks to Patrole

This patch:
  - Adds hacking check to Patrole (executed via tox -e pep8)
  - Corrects a few hacking errors
  - Adds hacking documentation to Patrole

Change-Id: Id43e24060a5290df91c594df6a38ba0cb239bbaf
diff --git a/patrole_tempest_plugin/rbac_policy_parser.py b/patrole_tempest_plugin/rbac_policy_parser.py
index 8256889..d4e989b 100644
--- a/patrole_tempest_plugin/rbac_policy_parser.py
+++ b/patrole_tempest_plugin/rbac_policy_parser.py
@@ -40,8 +40,7 @@
     each role, whether a given rule is allowed using oslo policy.
     """
 
-    def __init__(self, project_id, user_id, service=None,
-                 extra_target_data={}):
+    def __init__(self, project_id, user_id, service, extra_target_data=None):
         """Initialization of Rbac Policy Parser.
 
         Parses a policy file to create a dictionary, mapping policy actions to
@@ -64,6 +63,9 @@
         :param path: type string
         """
 
+        if extra_target_data is None:
+            extra_target_data = {}
+
         # First check if the service is valid
         service = service.lower().strip() if service else None
         self.admin_mgr = credentials.AdminManager()