[SPARK-4870] Add spark version to driver log

Author: Zhang, Liye <liye.zhang@intel.com>

Closes #3717 from liyezhang556520/version2Log and squashes the following commits:

ccd30d7 [Zhang, Liye] delete log in sparkConf
330f70c [Zhang, Liye] move the log from SaprkConf to SparkContext
96dc115 [Zhang, Liye] remove curly brace
e833330 [Zhang, Liye] add spark version to driver log

core/src/main/scala/org/apache/spark/SparkContext.scala

@@ -172,6 +172,9 @@ class SparkContext(config: SparkConf) extends Logging with ExecutorAllocationCli
   private[spark] def this(master: String, appName: String, sparkHome: String, jars: Seq[String]) =
     this(master, appName, sparkHome, jars, Map(), Map())
 
+  // log out Spark Version in Spark driver log
+  logInfo(s"Running Spark version $SPARK_VERSION")
+  
   private[spark] val conf = config.clone()
   conf.validateSettings()