Address CR comments

1. We should log the new port that we are going to try on instead of just saying
   "Trying again"
2. The first line should be logged at WARN level, not Info.
3. If the exception message contains "Address already in use" we can just log the
   exception message at WARN.
4. If the exception is some other message, we should log it at ERROR, and pass
the exception to logError so that the entire stack trace is printed.

Author: ash211

core/src/main/scala/org/apache/spark/ui/JettyUtils.scala

@@ -194,11 +194,16 @@ private[spark] object JettyUtils extends Logging {
         case s: Success[_] =>
           (server, server.getConnectors.head.getLocalPort)
         case f: Failure[_] =>
+          val nextPort = (currentPort + 1) % 65536
           server.stop()
           pool.stop()
-          logInfo("Failed to create UI at port, %s. Trying again.".format(currentPort))
-          logInfo("Error was: " + f.toString)
-          connect((currentPort + 1) % 65536)
+          val msg = s"Failed to create UI on port :$currentPort. Trying again on port :$nextPort"
+          if(f.toString.contains("Address already in use")) {
+            logWarning(s"$msg - $f")
+          } else {
+            logError(msg, f.exception)
+          }
+          connect(nextPort)
       }
     }