Things like -n to specify the lines to show with systemctl and
journalctl accepts syntax like:
journalctl -n4
systemctl -n14
Previously, typing `-nXX <tab>` where XX is a number, zsh would try to
complete an integer. Now it will see the XX and use the _journalctl_none
completion. This is also how any of the single letter options that take
arguments work as well.
_hosts_or_user_at_host was used by 6 different completions, and
previously was in all 6 of those files. I moved it out to its own file,
_sd_hosts_or_user_at_host. This will be autoloaded for use in other
completion functions. It also allows external completions to use this
function by simply calling _sd_hosts_or_user_at_host as in the systemd
completions.
