Improve security.setuidOwners usage

Using the "source" attribute prevents weird error messages if "program"
is not in environment.systemPackages. Another way to look at it is that
now the setuidOwners block is self contained.
Remove vsftpd service

I'm not using it.
transmission-service: tweak rpc-whitelist
munin-service: simplify network filter

The 'cidr_allow' format is more readable than 'allow' (regexp).