bsdinstall: Only show menu if there are more items to be installed

Obtained from: Rubicon Communications, LLC ("Netgate")
Sponsored by: Rubicon Communications, LLC ("Netgate")

(cherry picked from commit 95f0da5be1e3456c930f5f9538cbc099c65f2014)

Git Hash: 27988b8333007d319eb9e9929bda787c5012e59e
Git Author: renato@netgate.com

MFC r328839:

Add the ThinkPad X1 (sandybridge) to the bsdinstall blacklist

Reviewed by: AllanJude (for mfc)

MFC: r319863
bsdinstall: Make ZFS min_auto_ashift adjustment persistent

MFC: r319864
bsdinstall: support Auto ZFS mode for ARM64

Approved by: re (gjb)

MFC r313448:

bsdinstall: Make sure chroot filesystems are umounted after use

* DISTDIR_IS_UNIONFS is set every time BSDINSTALL_DISTDIR is mounted inside
BSDINSTALL_CHROOT. Use this flag to decide if it needs to be umounted
* BSDINSTALL_CHROOT/dev is mounted when 'bsdinstall mount' is called, there is
no need to mount it again when user goes to shell after installation

Reviewed by: allanjude
Obtained from: pfSense
MFC after: 1 week
Sponsored by: Rubicon Communications (Netgate)
Differential Revision: https://reviews.freebsd.org/D8573

MFC r302897:

Add new System Hardening menu and options to bsdinstall.

This patch add new 'hardening' file responsible for new bsdinstall
'System Hardening' menu allowing users to set some sane and carefully
picked system security options (like random process id's, hiding
other users/groups processes and others).

All options are OFF by default in this patch due to POLA principle
with intention to turn change some of them to ON by default in future.

Reviewed by: adrian, allanjude, bdrewery, nwhitehorn
Approved by: re@, adrian, allanjude