[1.9,2.x] doesn't let you set a database port

[Andreas Hasenack]

I have a situation where I need MAAS to talk to postgresql on port 5433 instead of the default 5432.

In MAAS 1.8, this was exposed in the django settings file in /etc/maas.

In MAAS 1.9, the closest setting file is /etc/maas/regiond.conf, but it has no database_port setting, just host and some others:
atabase_host: localhost
database_name: maasdb
database_pass: secret
database_user: maas
maas_url: http://10.245.200.25/MAAS

maas/settings.py has an empty setting for it:
    DATABASES = {
        'default': {
            'ENGINE': 'django.db.backends.postgresql_psycopg2',
            'NAME': config.database_name,
            'USER': config.database_user,
            'PASSWORD': config.database_pass,
            'HOST': config.database_host,
            'PORT': '',
        }

And maasserver/config.py needs to have database_port in RegionConfiguration, then we can add it to the settings file above.