Add two crude controls to allow the user to change how virtual nodes
are packed 1) Add trivial_ok flag to virt_lans table. Global to the lan or link, allow nodes in the lan or link to be colocated on the same phys node. Perhaps make it per-node at some point. 2) Add multiplex_factor to the experiments table to allow user to override the multiplex_factor that is contained in the node_types table. Make per type at some point.