Add serveraliases to the spotlight internal vhost

Currently GOV.UK routes to spotlight.performance.service.gov.uk

Ideally, we would like it route to spotlight.production.performance...

This commit adds nginx config for serveraliases for spotlight. In dev,
preview and staging this will add a duplicate server entry which generates
nginx warnings:

2013/12/05 13:25:49 [warn] 17355#0: conflicting server name "spotlight.development.performance.service.gov.uk" on 0.0.0.0:80, ignored
2013/12/05 13:25:49 [warn] 17355#0: conflicting server name "spotlight.development.performance.service.gov.uk" on 0.0.0.0:443, ignored

But in production the two server names will be different. Once GOV.UK
Puppet has been deployed to route to the production vhost, this duplication
can be removed on our end.

This same duplication occurs in the DNS CNAME.
Merge pull request #172 from alphagov/start-moving-spotlight-to-internal-vhost

Add serveraliases to the spotlight internal vhost