fix for https://spark-project.atlassian.net/browse/SPARK-1052

Author: Bijay Bisht <bijay.bisht@gmail.com>

Closes #568 from bijaybisht/SPARK-1052 and squashes the following commits:

da70395 [Bijay Bisht] fix for https://spark-project.atlassian.net/browse/SPARK-1052 - comments incorporated
fdb1d94 [Bijay Bisht] fix for https://spark-project.atlassian.net/browse/SPARK-1052

core/src/main/scala/org/apache/spark/scheduler/cluster/mesos/MesosSchedulerBackend.scala

@@ -130,13 +130,8 @@ private[spark] class MesosSchedulerBackend(
   private def createExecArg(): Array[Byte] = {
     if (execArgs == null) {
       val props = new HashMap[String, String]
-      val iterator = System.getProperties.entrySet.iterator
-      while (iterator.hasNext) {
-        val entry = iterator.next
-        val (key, value) = (entry.getKey.toString, entry.getValue.toString)
-        if (key.startsWith("spark.")) {
-          props(key) = value
-        }
+      for ((key,value) <- sc.conf.getAll) {
+        props(key) = value
       }
       // Serialize the map as an array of (String, String) pairs
       execArgs = Utils.serialize(props.toArray)