Move the ntp check to be on each server

Rather than having lots of checks on the monitoring server that all do
the same thing.
Merge pull request #578 from alphagov/move-ntp-to-be-per-server

Move the ntp check to be on each server
Check skew more frequently

There have been a few alerts show up on clock skew, but by the time of
checking them they are resolved. We may also need to tune the warning /
critical threshold, but this change means minor clock skew shouldnt
end up with critical production alerts for 1 hour after the case (until
the check runs again)
Merge pull request #579 from alphagov/check-ntp-more-frequently

Check skew more frequently
Add collectd plugin for ntpd

The intention is to give a bit more context around the ntp drift alerts.
Merge pull request #580 from alphagov/add-ntp-collectd

Add collectd plugin for ntpd
Remove Nick Gravgaard from Puppet
Remove users with 'ensure: absent' set

These users have all been deployed out to production, so they
can be removed from this hieradata.
Merge pull request #581 from alphagov/remove-nick-g

Remove Nick G
Monitor the postgresql secondary machine

Because, you know, having some insight into whether it is alive is a
good idea.
Merge pull request #582 from alphagov/monitoring-pg-secondary

Monitor the postgresql secondary machine
Add ipython on the development role
Merge pull request #583 from alphagov/ipython-development

Add ipython on the development role
Use nginx version from our PPA everywhere

* remove nginx Apt repo so that later versions aren't installed
* use our version (from ubuntu repo)

This is preparatory work so that we can use nginx-extra and thus use
lua/Perl to do stuff.
Merge pull request #584 from alphagov/feature/consistent-nginx-version

Use nginx version from our PPA everywhere