Rewrite some of the disk setup documentation to be clearer and contain
less obsolete information. Also move the entropy command down the list --
the list is ordered by likelihood of use rather than alphabetically.

MFC after:	1 week
Merge remote-tracking branch 'freebsd/master' into hardened/current/master
Merge remote-tracking branch 'origin/hardened/current/master' into hardened/current/segvguard