This is a follow-up of #10717 to use the same naming convention as on
Linux guests, in order to reduce the diffs.
Also adds the missing capability to `unmount_virtualbox_shared_folder`
on FreeBSD guests.
Since the virtualbox guest additions seem to only be available for
freeBSD, move the shared folder functionality over to freebsd guests
rather than all BSD guests.
Run remote rsync as root to guarantee that rsync can write to guestpath.
This obviates the need to chown the guestpath to the SSH user prior to
sync.
This brings a substantial speedup (2x on a moderately-sized shared
folder) and properly triggers filesystem notifications on only the files
changed by a given sync.
I don't use `activated` here because I'd really like to optimize
performance as much as possible, and loading files from disk is
generally slow. So instead of using `activated` I load the file at the
last possible moment which is when the exact class is being requested.
I don't think many people will do this outside of the core, and I'm not
too concerned.
