Set external_lb_address to eth0's address in all-in-one build

This patch sets the external_lb_address to the instance's eth0 address
to ensure that any services that rely on accessing that address are able
to do so.

Change-Id: Ie5955eaedef14f5916ec19203f8724e107a409da
Closes-Bug: #1404305
Merge "Set external_lb_address to eth0's address in all-in-one build"