Hi Rajesh,
I know only about 1 public network auto installation via Fuel.
Anyhow, Public / external networks are under Mirantis development and maintenance, so I think it's better to ask in Questions : Fuel for OpenStack .
Please put me as a subscriber in the question in Launchpad, I don't think there should be any special driver issues with doing so, since you have the others networks working over our interfaces.
Mirantis connects the private networks to a router with a gateway to their (only) public network, so you need to think about this point IMO.
Another option is just do it manually, but it's not so scalable...
Let's try the LP channel - let me know if you need any help with posting the question,
Aviram