trigger: fix custom tags

endpoints/trigger.py

@@ -629,18 +629,22 @@ class CustomBuildTrigger(BuildTrigger):
     return config
 
   def manual_start(self, trigger, run_parameters=None):
-    for parameter in ['branch_name', 'commit_sha',]:
+    for parameter in ['commit_sha']:
       if parameter not in run_parameters:
-        raise TriggerStartException
+        raise TriggerStartException('missing required parameter')
 
+    config = get_trigger_config(trigger)
     dockerfile_id = None
     branch = run_parameters.get('branch_name', None)
-    tags = {branch} if branch is not None else {}
+
+    tags = {branch}
+    if branch == 'master':
+      tags.add('latest')
+
     build_name = 'HEAD'
     metadata = {
       'commit_sha': run_parameters['commit_sha'],
-      'default_branch': branch,
-      'ref': 'refs/heads/%s' % branch,
+      'git_url': config['build_source'],
     }
 
-    return dockerfile_id, tags, build_name, trigger.config['subdir'], metadata
+    return dockerfile_id, list(tags), build_name, config['subdir'], metadata