Devstack automatically detect the public network interface when it is installed. If you have multiple interfaces available in your virtual machine and you want to set an IP on which openstack should start, then add an entry in local.conf:

HOST_IP=x.y.z.w

The IP should match the IP on any one of your network interface. If you are talking about starting on IP that is outside VM(i.e on host you are running your VM) then it can not be done, Yes you can use port forwarding provided by Virtualization software you are using.