Add ability for triggers to be disabled

Will be used in the followup commit to automatically disable broken triggers

endpoints/test/test_webhooks.py

@@ -0,0 +1,24 @@
+import base64
+import pytest
+
+from flask import url_for
+
+from data import model
+from endpoints.test.shared import conduct_call
+from test.fixtures import *
+
+def test_start_build_disabled_trigger(app, client):
+  trigger = model.build.list_build_triggers('devtable', 'building')[0]
+  trigger.enabled = False
+  trigger.save()
+
+  params = {
+    'trigger_uuid': trigger.uuid,
+  }
+
+  headers = {
+    'Authorization': 'Basic ' + base64.b64encode('devtable:password'),
+  }
+
+  conduct_call(client, 'webhooks.build_trigger_webhook', url_for, 'POST', params, None, 400,
+               headers=headers)