ownCloud 8.1.1's autoconfig resets trusted_domains / update trusted_domains if PRIMARY_HOSTNAME changes

Seems like ownCloud 8.1.1 now doesn't play nice with trusted_domains. Whatever is put in ahead of time gets reset to an array containing 'localhost' only, probably because we invoke autoconfiguration from the command line where it doesn't know the hostname it's being accessed from. We now set this value after running autoconfig.

This has the added benefit of also fixing the problem that if PRIMARY_HOSTNAME changes, trusted_domains wasn't updated. Now it is. Fixes #503.

See #514.