Configure /etc/network/interface with the right dhcp interface

Change-Id: I06c29c8d1369c506eeb27f8ae057f0889f2ac9c4
Reviewed-on: https://review.gerrithub.io/374164
Reviewed-by: Dennis Dmitriev <dis.xcom@gmail.com>
Tested-by: Dennis Dmitriev <dis.xcom@gmail.com>
diff --git a/tcp_tests/templates/physical_mcp11_ovs_dpdk/underlay--user-data.yaml b/tcp_tests/templates/physical_mcp11_ovs_dpdk/underlay--user-data.yaml
index e1646cd..1141993 100644
--- a/tcp_tests/templates/physical_mcp11_ovs_dpdk/underlay--user-data.yaml
+++ b/tcp_tests/templates/physical_mcp11_ovs_dpdk/underlay--user-data.yaml
@@ -69,6 +69,15 @@
    ########################################################
 
   write_files:
+   - path: /etc/network/interfaces
+     content: |
+          # The loopback network interface
+          auto lo
+          iface lo inet loopback
+
+          auto {interface_name}
+          iface {interface_name} inet dhcp
+
    - path: /etc/udev/rules.d/70-persistent-net.rules
      owner: root:root
      permissions: '0644'