daemon: add long_opts

Long options improve readability of scripts, makes code comprehension
easier. This patch adds long options while preserving the existing CLI
interface.

Also --help/-h option is added.

Reviewed by: allanjude, pauamma (both earlier versions), kevans
Differential Revision: https://reviews.freebsd.org/D38244

(cherry picked from commit 0a402ad2e6d6014ed8c622a90153f53b99c1b482)