Since all post-installkernel steps are assumed to operate in the updated
installation, it's necessary to chroot all of the followup steps in the new
boot environment. Set up and mount the source and object directories at the
same paths inside the BE root, and clean up to the extent changes were made.
This commit fixes upgrading using beinstall past the new ntpd user change.
Improve testability of changes to this script while I'm here.
Reported by: rpokala (earlier patch)
This is meant to install a new BE (boot environment) given a fully built
world/kernel. In addition to installing world and kernel in the new BE,
it also automatically performs /etc updates (using etcupdate or mergemaster)
and package updates (using pkg).
Because this process is performed in a new BE, it reduces the need for a
second reboot. It also means a reboot into a partially updated system (due
to install or hardware failure) can't happen.
Inspired by and similar in function to Solaris/illumos-style upgrades.
