DHCP Config changes + null pointer checks + ONOS-2881

Change-Id: Ice391f539ae816329fde7970d762380a36fd7661
diff --git a/apps/dhcp/src/test/resources/dhcp-cfg.json b/apps/dhcp/src/test/resources/dhcp-cfg.json
index 8ce5486..abc48a8 100644
--- a/apps/dhcp/src/test/resources/dhcp-cfg.json
+++ b/apps/dhcp/src/test/resources/dhcp-cfg.json
@@ -11,9 +11,7 @@
         "ttl": "63",
         "lease": "300",
         "renew": "150",
-        "rebind": "200"
-      },
-      "dhcpstore" : {
+        "rebind": "200",
         "delay": "3",
         "timeout": "150",
         "startip": "10.0.0.110",