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.