Exception and Preconditions Netconf Refactoring

Change-Id: I3cb4abee2c70138e37160b68418e71bb5f52e1a5
diff --git a/protocols/netconf/ctl/src/main/java/org/onosproject/netconf/ctl/NetconfStreamThread.java b/protocols/netconf/ctl/src/main/java/org/onosproject/netconf/ctl/NetconfStreamThread.java
index 1ed3f39..f003f7b 100644
--- a/protocols/netconf/ctl/src/main/java/org/onosproject/netconf/ctl/NetconfStreamThread.java
+++ b/protocols/netconf/ctl/src/main/java/org/onosproject/netconf/ctl/NetconfStreamThread.java
@@ -202,7 +202,7 @@
                     }
                 }
             } catch (IOException e) {
-                log.warn("Error in reading from the session for device " + netconfDeviceInfo, e);
+                log.warn("Error in reading from the session for device {} ", netconfDeviceInfo, e);
                 throw new RuntimeException(new NetconfException("Error in reading from the session for device {}" +
                                                                         netconfDeviceInfo, e));
                 //TODO should we send a socket closed message to listeners ?