Update the voltha code to make use of the interface option and add
a new voltha swarm file.

Change-Id: Icf2bd5a35aea3a8aa55de58acb56bfa6f4b34e0d
diff --git a/common/utils/nethelpers.py b/common/utils/nethelpers.py
index b79d2b0..a082eeb 100644
--- a/common/utils/nethelpers.py
+++ b/common/utils/nethelpers.py
@@ -22,7 +22,6 @@
 
 import netifaces as ni
 
-
 def get_my_primary_interface():
     gateways = ni.gateways()
     assert 'default' in gateways, \
@@ -36,10 +35,13 @@
 
 
 def get_my_primary_local_ipv4(ifname=None):
-    ifname = get_my_primary_interface() if ifname is None else ifname
-    addresses = ni.ifaddresses(ifname)
-    ipv4 = addresses[AF_INET][0]['addr']
-    return ipv4
+    try:
+        ifname = get_my_primary_interface() if ifname is None else ifname
+        addresses = ni.ifaddresses(ifname)
+        ipv4 = addresses[AF_INET][0]['addr']
+        return ipv4
+    except Exception as e:
+        return None
 
 
 if __name__ == '__main__':