Replace rule/expected_error_code with non-deprecated versions

This patch set replaces deprecated occurrences of rule with
rules and expected_error_code with expected_error_codes in
rbac_rule_validation.action decorator.

Along with removing the parameters from the decorator, all the
API tests have been changed to use the non-deprecated parameters
instead. Unit tests have also been updated.

Change-Id: I6485b6c57795b5fe75e2b339d5c9720da30be564
diff --git a/patrole_tempest_plugin/rbac_utils.py b/patrole_tempest_plugin/rbac_utils.py
index 366e033..6db2199 100644
--- a/patrole_tempest_plugin/rbac_utils.py
+++ b/patrole_tempest_plugin/rbac_utils.py
@@ -83,7 +83,7 @@
         Example::
 
             @rbac_rule_validation.action(service='test',
-                                         rule='a:test:rule')
+                                         rules=['a:test:rule'])
             def test_foo(self):
                 # Allocate test-level resources here.
                 with self.rbac_utils.override_role(self):