UpdateDjango 'sites' with real host

This will populate ```/admin/sites/site/1/``` with the real hostname during installation (Django default is example.com)

See: https://bugs.launchpad.net/oq-platform/+bug/1378372

Completes: #249 
Maybe better:
```
def baseenv(host, hazard_calc_addr, risk_calc_addr, oq_engserv_key,
            oq_secret_key, oq_bing_key='', db_name='oqplatform',
            db_user='oqplatform', db_pass=DB_PASSWORD,
            mediaroot='/tmp', staticroot='/home'):```