Collapse the override interface.vpp files

These interfaces follow a clear pattery of daisychaining and can be
computed using {{node.id}} and {{lab.id}}.

TESTED: Generating a new output has only expected diffs in the comments,
not in any IP or MTU or state values.

build/default/hvn2.lab.ipng.ch/vpp2-0/etc/vpp/config/interface.vpp

@@ -1,4 +1,4 @@
-comment { Gi10/0/0 is connected to the IPng Networks lab uplink }
+comment { Gi10/0/0 is connected to lab.ipng.ch:lab2 }
 set interface mtu 9000 GigabitEthernet10/0/0 
 set interface mtu packet 1500 GigabitEthernet10/0/0
 set interface ip address GigabitEthernet10/0/0 2001:678:d78:221::0:fffe/112