userboot: support environment and symlinks in test application

Pass the environment on to the loader.
Also define USERBOOT=1 in the environment varables.

Add support for symlinks in the test application open callback.

stat the root directory when opening file
Without this, running "ls" command on the root directory encounters
issues getting the directory listing.

Reviewed by: jhb
Obtained from: Juniper Networks, Inc.
Differential Revision: https://reviews.freebsd.org/D44625

Remove $FreeBSD$: two-line .h pattern

Remove /^\s*\*\n \*\s+\$FreeBSD\$$\n/

test_diskread(): detect end of the disk

Detect the end of the disk condition. This may happpen when
disk image is truncated and the reads are addressing blocks past
image end.

MFC after: 1 week
Differential Revision: https://reviews.freebsd.org/D35432

loader: zfs should support bootonce an nextboot

bootonce feature is temporary, one time boot, activated by
"bectl activate -t BE", "bectl activate -T BE" will reset the bootonce flag.

By default, the bootonce setting is reset on attempt to boot and the next
boot will use previously active BE.

By setting zfs_bootonce_activate="YES" in rc.conf, the bootonce BE will
be set permanently active.

bootonce dataset name is recorded in boot pool labels, bootenv area.

in case of nextboot, the nextboot_enable boolean variable is recorded in
freebsd:nvstore nvlist, also stored in boot pool label bootenv area.
On boot, the loader will process /boot/nextboot.conf if nextboot_enable
is "YES", and will set nextboot_enable to "NO", preventing /boot/nextboot.conf
processing on next boot.

bootonce and nextboot features are usable in both UEFI and BIOS boot.

To use bootonce/nextboot features, the boot loader needs to be updated on disk;
if loader.efi is stored on ESP, then ESP needs to be updated and
for BIOS boot, stage2 (zfsboot or gptzfsboot) needs to be updated
(gpart or other tools).

At this time, only lua loader is updated.

Sponsored by: Netflix, Klara Inc.
Differential Revision: https://reviews.freebsd.org/D25512

Fix pkgfs stat so it satisfies libsecureboot

We need a valid st_dev, st_ino and st_mtime
to correctly track which files have been verified
and to update our notion of time.

ve_utc_set(): ignore utc if it would jump our current time
by more than VE_UTC_MAX_JUMP (20 years).

Allow testing of install command via userboot.
Need to fix its stat implementation too.

bhyveload also needs stat fixed - due to change to userboot.h

Call ve_error_get() from vectx_close() when hash is wrong.

Track the names of files we have hashed into pcr

For the purposes of measured boot, it is important
to be able to reproduce the hash reflected in
loader.ve.pcr
so loader.ve.hashed provides a list of names in the order they
were added.

Reviewed by: imp
MFC after: 1 week
Sponsored by: Juniper Networks
Differential Revision: https://reviews.freebsd.org//D24027

loader: userboot/test should accept more than one disk

allow to specify multiple -d options, test -d disk1 -d disk2 ..

userboot/test should use PRIx64 as one would expect from prefix 0x

Test is printing decimal value after prefix 0x.

Make putenv and getenv match the userland definition of these
functions, tweak man page and one variable that shouldn't be const
anymore.

Sponsored by: Netflix

Mark the func pointer as __dead2. It looks up loader_main, which
either aborts or exits, but never returns. Tag it as a non-returning
function rather than supply a bogus return(0) at the end of main.

CID: 1382885
Sponsored by: Netflix

Move sys/boot to stand. Fix all references to new location

Sponsored by: Netflix