Extract /etc/default/unicorn_$name from FreeBSD hosts

Only try to write /etc/default file if params::etc_default is true.
Add FreeBSD init script template

Included is a patch which fixes issues with _find_processes not
detecting “ruby19: unicorn” as the correct process entry. This issue is
currently referenced in FreeBSD PR conf/169047 from 2012 but has not
yet been closed. An updated patch has been provided to the bug-followup
address.
Allow initscript value to be determined by params