The Prime Sandboxes drop-in follows 0.4.7

Code written for prime-sandboxes 0.4.7 runs on withruntime.prime. Its new arch option on create works with "amd64", and "arm64" gets a plain error before any sandbox is made, as Runtime sandboxes are x86-64. create_lan_network now takes rules and, as before, names Runtime's private network instead. See Migrate.