Add 'vmadm' module which provides 'virt' for SmartOS

First commit of 'smartos_vmadm', a module that uses the 'vmadm'
command on SmartOS CN. For the moment very few functions are present
but I'm pretty sure that more will come in a couple of days.

Implemented :

* list_vms()

* list_active_vms()

* list_inactive_vms()

* shutdown(uuid)

* start(uuid)

* reboot(uuid)