network: fix mod_hostname() and arp() to work on OpenBSD.

arp(8) output has recently changed on OpenBSD and the hostname
is set under /etc/myname.
Merge branch 'obsd-network' of https://github.com/ajacoutot/salt into ajacoutot-obsd-network
use correct spacing
Merge pull request #15434 from thatch45/ajacoutot-obsd-network

Merge #15430