engine: resources: Clean up virt code

There was and still is a bunch of terrible mess in this code. This does
some initial cleanup, and also fixes an important bug!

If you're provisioning a vmhost from scratch, then the function engine
might do some work to get the libvirt related services running before
the virt resource is used to build a vm. Since we had connection code in
Init() it would fail if it wasn't up already, meaning we'd have to write
fancy mcl code to avoid this, or we could do this refactor and keep
things more logical.

modules/virtualization/main.mcl

@@ -50,7 +50,6 @@ class base() {
 	#}
 
 	# We want to use qemu of course!
-	# XXX: I had to run `systemctl start virtqemud` to get things working...
 	svc "virtqemud" {
 		state => "running",
 		startup => "enabled",