Fixes to resolve confusion between gotpl and bash variable handling
and also how bash handles empty strings.
These are required to robustly:
1. make use of an external network (for floating IPs)
2. specify *which* interface in the nodes is used for the tunnelled
traffic.
Change-Id: I30fd675cd471a77dc09a6c7f6ee81120a978b38b
7b96c5cfff