Have the builder not start and stop, over and over, if not enabled

buildman/builder.py

@@ -21,6 +21,8 @@ EXTERNALLY_MANAGED = 'external'
 def run_build_manager():
   if not features.BUILD_SUPPORT:
     logger.debug('Building is disabled. Please enable the feature flag')
+    while True:
+      time.sleep(1000)
     return
 
   build_manager_config = app.config.get('BUILD_MANAGER')