Support machine placement in bundle export

* Service placement on machines is based on unit placement, per deployer requirements.
* LXC, though partially implemented, is not officially supported because deployer support is spotty.
I'll update to parentId since we will try to support KVM in the future, but right now we can't support kvm at all (as opposed to our unofficial, not very good lxc support) b/c deployer syntax doesn't understand it.