Validate audit template UUID on audit create

The audit template UUID should be validated during the creation of an
audit.  An HTTP 400 error is returned to the client if an invalid audit
template UUID is passed as part of the body when creating an audit.

APIImpact
Closes-Bug: #1510188

Change-Id: I0543d22751b77f6641ddef6a7f0f4acce61180fd

watcher/tests/api/v1/test_audits.py

@@ -451,6 +451,24 @@ class TestPost(api_base.FunctionalTest):
             response.json['created_at']).replace(tzinfo=None)
         self.assertEqual(test_time, return_created_at)
 
+    @mock.patch('oslo_utils.timeutils.utcnow')
+    def test_create_audit_invalid_audit_template_uuid(self, mock_utcnow):
+        test_time = datetime.datetime(2000, 1, 1, 0, 0)
+        mock_utcnow.return_value = test_time
+
+        audit_dict = post_get_test_audit()
+        # Make the audit template UUID some garbage value
+        audit_dict['audit_template_uuid'] = (
+            '01234567-8910-1112-1314-151617181920')
+
+        response = self.post_json('/audits', audit_dict, expect_errors=True)
+        self.assertEqual(400, response.status_int)
+        self.assertEqual("application/json", response.content_type)
+        expected_error_msg = ('The audit template UUID or name specified is '
+                              'invalid')
+        self.assertTrue(response.json['error_message'])
+        self.assertTrue(expected_error_msg in response.json['error_message'])
+
     @mock.patch.object(deapi.DecisionEngineAPI, 'trigger_audit')
     def test_create_audit_doesnt_contain_id(self, mock_trigger_audit):
         mock_trigger_audit.return_value = mock.ANY