After 4ee8fed systems hang on shtudown until systemd times out.

Do not wait for NIS on shutdown.
Tell systemd to order nis and mxstartup in startup and shutdown

migrated from NIS to hostconfig

Restart not needed

Regard the 4th column of /etc/mxstartups as the name of a systemd
service unit if it ends in ".service".  In that case, ignore the
username and use systemctl to start/stop that unit.

The idea is to use /etc/mxstartups for services, which we want to run as
a systems service, e.g. to use the features of systemd. Currently there
is an option to use unit files with an encoded hostname but we prefer to
have the information of which hosts starts which service in
/etc/mxstartups.