Add support for adjusting etcd ttl on job_heartbeat. Switch the heartbeat method to a coroutine.

buildman/manager/executor.py

@@ -142,6 +142,7 @@ class EC2Executor(BuilderExecutor):
     if builder_id not in [si.id for si in stopped_instances]:
       raise ExecutorException('Unable to stop instance: %s' % builder_id)
 
+
 class PopenExecutor(BuilderExecutor):
   """ Implementation of BuilderExecutor which uses Popen to fork a quay-builder process.
   """