prepare wmf-beta-autoupdate to be launched by Jenkins

This let wmf-beta-autoupdate to be run by a Jenkins job. It removes the
upstart wrapper and the script is no more looping indefinitely. It now
as to be run from time to time as user mwdeploy, which is what Jenkins
is going to do.

That would let people retrigger the update easily and provide a public
log of the run for other to investigate.

Change-Id: I0d9cc6162787f011249717803bad622d58f64eec