Bridged network adapter for Packer + VirtualBox?
With a bridged adapter, your VM would get its IP from the host machine's network DHCP server. This would allow it to be pinged from your internal network. 

I'd also specify in your configuration that your cable is connected as so:

VBoxManage modifyvm "VM" --cableconnected1 on


Port forwarding in the VM's configuration would also work. It would allow access from the host machine's IP by just specifying the forwarded port.

To forward port 22 to 2222 you would do as so: 

VBoxManage modifyvm "VM" --nic1 nat
VBoxManage modifyvm "VM" --natpf1 "guestssh,tcp,,2222,,22"
VBoxManage modifyvm "VM" --cableconnected1 on


If you want it to be accessible by the internet, you would need do port forwarding on your router to route access from your public ip:port to your internal ip:port.