Override network_topology template

DHC-1261

Change-Id: I0e52043c3c27442d556b9e06cec19f76856cdf8e
Signed-off-by: Rosario Di Somma <rosario.disomma@dreamhost.com>
Merge pull request #20 from rodis/dhc-1261-fix-network-topology

Override network_topology template