network: Fix error handling for 'kill -HUP'

When 'kill' execution fails for some reason (e.g. permission denied) we should
not continue with relunching dnsmasq.
rootwrap: use CommandFilter for 'kill' and not KillFilter

This is a workaround for FreeBSD because rootwrapper KillFilter is Linux
specific: it's based on parsing /proc/... entries, which leads to unmatched
filter condition on != Linux platforms.
rootwrap: clean up compute filters file a bit