Rotate performanceplatform-collector logs

They're currently not being rotated and are getting pretty darned big
Merge pull request #520 from alphagov/rotate-collector-logs

Rotate performanceplatform-collector logs
Monitor lumberjack app processes

If one of the lumberjack processes crashes fire a sensu alert. They are
managed with upstart so they usually come back up again. However, if
they crash coming up again too often upstart will leave them down.