Add Jenkins cleanup thread.

It searches for outstanding builds that haven't reported back
or otherwise can't be found by Jenkins, and marks them complete
with a result of "LOST".  This should help to avoid deadlocks
where Zuul waits forever to hear back from Jenkins after missing
a notification.

Add pyflakes to tox.ini.

Change-Id: I26d3fbf375e82e224448ec3337f9cc97deeccd56
4 files changed