Uninstall puppet before running puppet jobs

Some versions of Puppet (2.7.x) do not like when an other
version of Puppet (3.x) is installed at the same time, resulting
in this kind of errors:

    cannot load such file -- windows/error

Uninstalling and purging the system version of Puppet
will prevent such conflicts from happening.

Change-Id: I70aa291f0966fac4d7f32df4573eb164c1d5fccd
Merge "Uninstall puppet before running puppet jobs"