Use explicit defaults for NTP checks

Using the defaults as in https://github.com/sensu/sensu-community-plugins/blob/c6cef387d980e17ba4e493f9cd48671c3b66ecf7/plugins/system/check-ntp.rb
but having the explicitly here so that people don’t have to go looking
elsewhere for the values.

I’ve asked in the #sensu channel on freenode for more documentation
about the the check-ntp plugin, but for now, this should quieten our
alerts and we can tune them in the future.
Puppet lint corrections
Autofix puppet lint that we can
Fix namespace warnings
Merge pull request #587 from alphagov/feature/lint

Clean up puppet
Add a request ID to all the things

As person responsible for operating software in production
I would like to have a unique ID associated with every request
So that it is easy for me to track down problems in a distributed
system.

This is the first step to that. Every request coming in to our SSL
termination machines will have a UUID assigned to it with an HTTP
header.

We can then amend our logging to include this header where appropriate
and make it easier to trace requests going through the system.

This removes nginx-full and replaces it with nginx-extras.