Today I released a power driver to manage VirtualBox VMs power automatically by MAAS. This driver is based on the MAAS power webhook. You can clone it from my github.
https://github.com/ssbostan/vboxpower
https://medium.com/@ssbostan/maas-integration-with-virtualbox-20d850381c21
All contributions are welcomed. If you find any bugs, please file an issue.
Enjoy it.