Idempotent networking setup, other minor fixes.

The host only networking interface name has a prefix appended to the key
that comes back from Machine.HostonlyNets & virtualbox.DHCPs. Using
these to match the current configured networking entities for
idempotency.

Hard-linking the image file because Virtualbox likes to delete it along
with the virtual machine. This is usually not what you want for a cached
cloud image.

Starting the machine after creating/matching it.

Conflicts:
	main.go
Merge remote-tracking branch 'origin/master'

Configure & set hostonly net on existing net for new machine.

Conflicts:
	main.go