Use master.password file and format on freebsd platform

[rtgnx]

FreeBSD uses slightly different format for it's user database master.passwd(5)
This change will use ${BASE}/master.passwd on freebsd build targets.
Before merging this, there's another pr to the-maldrige/shadow #1 with necessary changes to the format.

I have tested this on two freebsd hosts.

[rtgnx]

Additionally for the system to actually pick up the changes a call to pwd_mkdb(8) is required

 $:pwd_mkdb -p /etc/master.passwd

I am not sure if you'd prefer to leave that up to the user or include this in the change, since normally this would be run
as a cron job and can be easily made into something like */2 * * * * localize && pwd_mkdb -p /etc/master.passwd