Pass local IP address instead of hostname in spark.master.host. Fixes #117.

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

@@ -42,7 +42,7 @@ class SparkContext(
 
   // Set Spark master host and port system properties
   if (System.getProperty("spark.master.host") == null) {
-    System.setProperty("spark.master.host", Utils.localHostName)
+    System.setProperty("spark.master.host", Utils.localIpAddress)
   }
   if (System.getProperty("spark.master.port") == null) {
     System.setProperty("spark.master.port", "7077")