Add option to bsdinstall to disable insecure console, update stack guard option

This patch adds new bsdinstall option to hardening section that allows users
to change this behaviour to secure one and updates stack guard option so it
would set the value of relevant sysctl to 512 (2MB)

Submitted by: Bartek Rutkowski
Reviewed by: adrian, bapt, emaste
Approved by: bapt, emaste
MFC after: 1 day
Sponsored by: Pixeware LTD
Differential Revision: https://reviews.freebsd.org/D9700