Add serveraliases to the spotlight internal vhost

Currently GOV.UK routes to `spotlight.performance.service.gov.uk` in production.

Ideally, I think we would like it route to `spotlight.production.performance.service.gov.uk` to indicate that this is not a public-facing `service.gov.uk` subdomain.

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 on reload:

    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.

Let me know if you think this is not a good approach or if the effort involved is not worth it. I'm trying to clear out a bit of tech debt before it gets too old.