Net: Add `nat.rb`

The `nat.rb` file is a ruleset used to configure NAT rules on the vShield Edge
firewall. This commit adds this file.
Box: Add YAML file for use when launching boxes

The YAML file in this commit is used when launching new GOV.UK off-site backup
machines using `vcloud-launch`.
Box: Add `jenkins.sh` for use when launching boxes

This commit adds a `jenkins.sh` box for use when launching boxes using
`vcloud-launch` and a one-click Jenkinsified installation.
Remove `lb` component from `jenkins.sh`

This commit removes the `lb` component from the Jenkins file as we do not need
to load-balance requests to/from the off-site backup machines. Therefore,
removing the `lb` component will ensure that we don't run this automatically
(and run in to errors, given that the lb.rb file does not exist in this
repository) when the job is Jenkinsified and run automagically.