Backport test case improvements

Add random primary key mixin. Split test case code into mixins.
Make the view test case and the API test cases part of the same
class hierachy. Update tests that failed due to the new import
locations.

Signed-off-by: Roberto Rosario <roberto.rosario.gonzalez@gmail.com>

mayan/apps/permissions/tests/mixins.py

@@ -0,0 +1,8 @@
+from __future__ import unicode_literals
+
+
+class RoleTestCaseMixin(object):
+    def grant_permission(self, permission):
+        self.role.permissions.add(
+            permission.stored_permission
+        )