Closes-Bug: #1597190 - Default gateway is being set as empty in SM Li…

…te by default

Previously we were handling case where default gateway key in missing from JSON
But SM Lite generated server JSONS have this key but have value as empty
This scenario needs to be handled

Change-Id: Ibd77c9fcc4fe5361b1ce6138754977dffc329573

src/server_mgr_main.py

@@ -3283,9 +3283,9 @@ def get_control_ip(self, server):
     def get_control_gateway(self, server):
         control_intf = eval(self.get_control_interface(server))
         for key, value in control_intf.iteritems():
-            if 'gateway' in value:
+            if 'gateway' in value and len(value['gateway']):
                 return str(IPNetwork(value['gateway']).ip)
-        if 'gateway' in server:
+        if 'gateway' in server and len(server['gateway']):
             return str(IPNetwork(server['gateway']).ip)
         else:
             return ''