Exception and Preconditions Netconf Refactoring

Change-Id: I3cb4abee2c70138e37160b68418e71bb5f52e1a5
diff --git a/providers/netconf/device/src/main/java/org/onosproject/provider/netconf/device/impl/NetconfDeviceProvider.java b/providers/netconf/device/src/main/java/org/onosproject/provider/netconf/device/impl/NetconfDeviceProvider.java
index 0bf3493..0a9c624 100644
--- a/providers/netconf/device/src/main/java/org/onosproject/provider/netconf/device/impl/NetconfDeviceProvider.java
+++ b/providers/netconf/device/src/main/java/org/onosproject/provider/netconf/device/impl/NetconfDeviceProvider.java
@@ -145,9 +145,8 @@
     public boolean isReachable(DeviceId deviceId) {
         NetconfDevice netconfDevice = controller.getNetconfDevice(deviceId);
         if (netconfDevice == null) {
-            log.debug("Requested device id: "
-                             + deviceId.toString()
-                             + "  is not associated to any NETCONF Device");
+            log.debug("Requested device id: {} is not associated to any " +
+                              "NETCONF Device", deviceId.toString());
             return false;
         }
         return netconfDevice.isActive();