Another example of slave not rebooting when asked to at the completion of a build.   Manually rebooted it and now it's back up and connected.

From the twistd.log:

2017-07-19 20:54:11-0700 [Broker,client] message from master: Received keepalive from master
2017-07-19 20:59:11-0700 [-] sending app-level keepalive
2017-07-19 21:04:11-0700 [-] sending app-level keepalive
2017-07-19 21:06:33-0700 [-] command finished with signal None, exit code 0, elapsedTime: 13477.807836
2017-07-19 21:06:33-0700 [-] SlaveBuilder.commandComplete <buildslave.commands.shell.SlaveShellCommand instance at 0x7fa08b2c2248>
2017-07-19 21:06:33-0700 [Broker,client] Setting needs_reboot flag
2017-07-19 21:06:33-0700 [Broker,client] slave shutting down on command from master
2017-07-19 21:06:34-0700 [-] firing system event shutdown
2017-07-19 21:06:34-0700 [-] calling before trigger: <bound method MultiService.stopService of <twisted.application.service.MultiService instance at 0x7fa08b658488>>
2017-07-19 21:06:34-0700 [-] stopping service <buildslave.bot.BuildSlave instance at 0x7fa08b658170>
2017-07-19 21:06:34-0700 [-] stopping service <twisted.application.internet.TCPClient instance at 0x7fa08b9dd560>
2017-07-19 21:06:34-0700 [-] stopped service <twisted.application.internet.TCPClient instance at 0x7fa08b9dd560>
2017-07-19 21:06:34-0700 [-] stopping service <buildslave.bot.Bot instance at 0x7fa08b658830>
2017-07-19 21:06:34-0700 [-] stopping service <SlaveBuilder 'android_nexus7_perf_bisect' at 140327488888560>
2017-07-19 21:06:34-0700 [-] stopped service <SlaveBuilder 'android_nexus7_perf_bisect' at 140327488888560>
2017-07-19 21:06:34-0700 [-] stopped service <buildslave.bot.Bot instance at 0x7fa08b658830>
2017-07-19 21:06:34-0700 [-] stopped service <buildslave.bot.BuildSlave instance at 0x7fa08b658170>
2017-07-19 21:06:34-0700 [-] calling during/after trigger: <bound method SelectReactor.crash of <twisted.internet.selectreactor.SelectReactor object at 0x7fa08abd4910>>
2017-07-19 21:06:34-0700 [-] calling during/after trigger: <bound method SelectReactor.disconnectAll of <twisted.internet.selectreactor.SelectReactor object at 0x7fa08abd4910>>
2017-07-19 21:06:34-0700 [Broker,client] lost remote
2017-07-19 21:06:34-0700 [Broker,client] Lost connection to master4.golo.chromium.org:8141
2017-07-19 21:06:34-0700 [Broker,client] Stopping factory <buildslave.bot.BotFactory instance at 0x7fa08b9dd440>
2017-07-19 21:06:34-0700 [-] calling during/after trigger: <function stop_timeseries_monitoring at 0x7fa08a7e0c08>
2017-07-19 21:06:34-0700 [-] calling during/after trigger: <bound method SelectReactor._stopThreadPool of <twisted.internet.selectreactor.SelectReactor object at 0x7fa08abd4910>>
2017-07-19 21:06:34-0700 [-] finished firing system event
2017-07-19 21:06:34-0700 [-] Main loop terminated.
2017-07-19 21:06:34-0700 [-] Server Shut Down.