Move checks into a subdirectory

We seemed to be trying to do namespacing with a _check suffix so I
thought it might be a plan to use real namespaces
Merge branch 'master' of github.com:alphagov/pp-puppet into upgrade-apt-packages
Enable unattended upgrades and add alerts

We have not been explicitly enabling unattended upgrades, which is
really not a good thing. This commit will enable them and also use
gds-nagios-plugins to alert on packages requiring reboot and if there
are security patches outstanding that need to be applied.
Merge pull request #220 from alphagov/upgrade-apt-packages

Upgrade apt packages