Adding Server aliases for the gis vhost

# Who should be looking at this?
@mattdebont @felixMasonJncc @nbnrain @NimChimpsky 

# What have I done?

Hey all, I realised that provisioning a nbngateway web server in production mode would not set up the gis[1-4].nbn.org.uk server aliases which are required by the IMT

I also wanted to demo how we can make changes like this to the webservers and review them before pushing to production.

# What would happen now?

The staging web server will automatically pick up the changes (on next puppet run) after we have merged in to master. If all is happy we can push to production using something like:

     puppet agent --test

You should also be able to check this code out on your vagrant machine, by either adjusting your puppetfile or checking out the branch within the vagrant machine.

In this case no changes on the development machine should occur as this is a fix for production