Move this Exec to a dedicated class that is not included by default i.e. we
default not to "apt-get update" on every Puppet run.
We now make use of this class in the apt::upgrade_package define to make sure
APT indexes are up-to-date before attempting package upgrades.
One may now use the following to ensure current packages are installed by
Package resources:
include apt::update
Package { require => Exec[apt_updated] }
