MFC r346545-r346546, r346680, r346700, r346705

r346545:
libbe(3): allow creation of arbitrary depth boot environments

libbe currently only provides an API to create a recursive boot environment,
without any formal support for intentionally limiting the depth. This
changeset adds an API, be_create_depth, that may be used to arbitrarily
restrict the depth of the new BE.

r346546:
libbe(3): Add a test for be creation

r346680:
libbe(3): Copy received properties as well

This was inherently broken on send|recv datasets.

r346700:
libbe(3): Fix mis-application of patch (SHLIBDIR)

Rob's patch in D18564 cemented the SHLIBDIR because bsd.own.mk (included by
src.opts.mk) sets it to /usr/lib. r346546 did somehow not apply this part of
the patch, leaving it to get installed to the wrong place and subsequently
removed via ObsoleteFiles.

r346705:
libbe(3): Fix libcompat build

SHLIBDIR should still be optionally set, just before src.opts.mk is included
so that libcompat can properly override it. This fixes lib32 failures
reported by both Jenkins and Michael Butler.

MFC bectl(8)/libbe(3): r337663-337664,337667,337697-337699,337800,337805,
337915-337918,337921,337924,337947,337993-337995,338221-338222,338303,
338417,339047,339972,339994,340334,340507-340508,340592-340594,
340635-340636,340722-340723,340974,342466,342849,342903,342911,343335,
343543,343977,343993-343994,344034,344067,344084,345302,345769,
345845-345846,345848,346082

There are simply too many small changes to enumerate; in summary:

bectl(8)/libbe(3) has been introduced from current state in -CURRENT and
added to the stable/11 rescue build. bectl(8) is a tool for managing ZFS
boot environments, largely inspired by beadm. It includes features such as
being able to jail a boot environment or easily mount it for modification.

Relnotes: probably

MFC r342362-r342363: config(8) duplicate option handling

r342362:
config(8): Allow duplicate options to be specified

config(8)'s option handling has been written to allow duplicate options; if
the value changes, then the latest value is used and an informative message
is printed to stderr like so:

/usr/src/sys/amd64/conf/TEST: option "VERBOSE_SYSINIT" redefined from 0 to 1

Currently, this is only a possibility for cpu types, MAXUSERS, and
MACHINE_ARCH. Anything else duplicated in a config file will use the first
value set and error about duplicated options on subsequent appearances,
which is arguably unfriendly since one could specify:

include GENERIC
nooptions VERBOSE_SYSINIT
options VERBOSE_SYSINIT

to redefine the value later anyways.

Reported by: mmacy

r342363:
config(8): Remove all instances of an option when opting out

Quick follow-up to r342362: options can appear multiple times now, so
clean up all of them as needed. For non-OPTIONS options, this has no effect
since they're already de-duplicated.