dd a new option (-H) to daemon(8) to catch SIGHUP and re-open output_file file when
received.

The default system log rotation mechanism (newsyslog(8)) requires ability to send
signal to a daemon in order to properly complete rotation of the logs in an "atomic"
manner without having to making a copy and truncating original file. Unfortunately
our built-in mechanism to convert "dumb" programs into daemons has no way to handle
this rotation properly. This change adds this ability, to be enabled by supplying -H
option in addition to the -o option.

Reviewed by: markj, rpokala (manpages)
MFC after: 2 weeks
Differential Revision: https://reviews.freebsd.org/D26526