Do not start puppet agent in Labs

Follow up to I69db5b1c9af3d3e1db66570337075e9d54850b29. It turns out
that I did not research the mechanism for running Puppet in labs well.
The existing Labs configuration runs `puppet agent` from cron three
times per hour rather than relying on a long running agent service.

Bug: 70421
Change-Id: Ie53f2ff0d714821ef7366e5a98654ff89ba16f88