libvirt-machine: Add a boolean 'run-in-bg' property
libvirt-machine: Add a boolean 'run-in-bg' property

This property dictates whether or not Boxes should automatically
pause/save the machine or not. By default this is set to false.

https://bugzilla.gnome.org/show_bug.cgi?id=746754

vbenes/gnome-boxes,vbenes/gnome-boxes