Looks like the builder never rebooted after it completed https://uberchromegw.corp.google.com/i/chromium.android/builders/KitKat%20Tablet%20Tester/builds/7447


From the master:

2017-04-28 13:14:44-0700 [-]  <Build KitKat Tablet Tester>: build finished
2017-04-28 13:14:44-0700 [-] PubSub: Status update (buildFinished): ('KitKat Tablet Tester', <BuildStatus #7447>, 2)
2017-04-28 13:14:44-0700 [-] pruning '/home/chrome-bot/buildbot/build/masters/master.chromium.android/KitKat_Tablet_Tester/4447'
2017-04-28 13:14:44-0700 [-] releaseLocks(<AutoRebootBuildSlave 'build42-b1', current builders: KitKat Tablet Tester>): []

From the slave:

2017-04-28 13:14:43-0700 [-] SlaveBuilder.commandComplete <buildslave.commands.shell.SlaveShellCommand instance at 0x7f47404c2560>
2017-04-28 13:14:44-0700 [Broker,client] Setting needs_reboot flag
2017-04-28 13:14:44-0700 [Broker,client] slave shutting down on command from master
2017-04-28 13:14:44-0700 [-] firing system event shutdown
2017-04-28 13:14:44-0700 [-] calling before trigger: <bound method MultiService.stopService of <twisted.application.service.MultiService instance at 0x7f47414feb00>>
2017-04-28 13:14:44-0700 [-] stopping service <buildslave.bot.BuildSlave instance at 0x7f47414fe950>
2017-04-28 13:14:44-0700 [-] stopping service <twisted.application.internet.TCPClient instance at 0x7f47414fe680>
2017-04-28 13:14:44-0700 [-] stopped service <twisted.application.internet.TCPClient instance at 0x7f47414fe680>
2017-04-28 13:14:44-0700 [-] stopping service <buildslave.bot.Bot instance at 0x7f47414fe908>
2017-04-28 13:14:44-0700 [-] stopping service <SlaveBuilder 'KitKat Tablet Tester' at 139943998180456>
2017-04-28 13:14:44-0700 [-] stopped service <SlaveBuilder 'KitKat Tablet Tester' at 139943998180456>
2017-04-28 13:14:44-0700 [-] stopped service <buildslave.bot.Bot instance at 0x7f47414fe908>
2017-04-28 13:14:44-0700 [-] stopped service <buildslave.bot.BuildSlave instance at 0x7f47414fe950>
2017-04-28 13:14:44-0700 [-] calling during/after trigger: <bound method SelectReactor.crash of <twisted.internet.selectreactor.SelectReactor object at 0x7f47419d7e10>>
2017-04-28 13:14:44-0700 [-] calling during/after trigger: <bound method SelectReactor.disconnectAll of <twisted.internet.selectreactor.SelectReactor object at 0x7f47419d7e10>>
2017-04-28 13:14:44-0700 [Broker,client] lost remote
2017-04-28 13:14:44-0700 [Broker,client] Lost connection to master1.golo.chromium.org:30101
2017-04-28 13:14:44-0700 [Broker,client] Stopping factory <buildslave.bot.BotFactory instance at 0x7f47414fe710>
2017-04-28 13:14:44-0700 [-] calling during/after trigger: <function stop_timeseries_monitoring at 0x7f4740a54ed8>
2017-04-28 13:14:44-0700 [-] calling during/after trigger: <bound method SelectReactor._stopThreadPool of <twisted.internet.selectreactor.SelectReactor object at 0x7f47419d7e10>>
2017-04-28 13:14:44-0700 [-] finished firing system event
2017-04-28 13:14:44-0700 [-] Main loop terminated.
2017-04-28 13:14:44-0700 [-] Server Shut Down.