Add support for save_config_on_stop on vm_manager #52
Description
The VirtualDomain save_config_on_stop option allows us to save the modification done on libvirt configuration when stopping.
This doesn't work on SEAPATH because configurations are stored in Ceph RBD metadata.
We need to update vm_manager to support it.
As an alternative, we can modify the save_condig function on VirtualDomain.