Add initial support for OpenBSD

 * Split code from freebsd.py to bsd.py
 * Make {Open,Net,Free}bsd classes inherit from Bsd
Add _check_enabled_sshd() for OpenBSD

Add a method that checks if the ssh daemon is enabled at boot.
Add _check_enabled_sshd() for NetBSD

Add a method that checks if the ssh daemon is enabled at boot.
Fill SORTORDER & KERNEL metadata for *BSD