Previously this was either 'vlan' or 'flat' depending on the external
network type, and there were also cases when the name and type were
mismatched - particularly when the flat network was untagged traffic
on a vlan bridge.
This patch removes that confusion and always names the external
network 'physnet1' to align with the upstream neutron examples.
Change-Id: I3cd8b93b42777b787552051bcdc9a90347f1e03d
563159f49c