Do not copy local jars given to SparkContext in yarn mode since the Context is...

Do not copy local jars given to SparkContext in yarn mode since the Context is not running on local. This bug causes failure when jars can not be found. Example codes (such as spark.examples.SparkPi) can not work without this fix under yarn mode.

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

@@ -102,6 +102,7 @@ class SparkContext(
   }
 
   private val isLocal = (master == "local" || master.startsWith("local["))
+  private val isYarn = (master == "yarn-standalone")
 
   // Create the Spark execution environment (cache, map output tracker, etc)
   private[spark] val env = SparkEnv.createFromSystemProperties(
@@ -577,11 +578,18 @@ class SparkContext(
     } else {
       val uri = new URI(path)
       val key = uri.getScheme match {
-        case null | "file" => env.httpFileServer.addJar(new File(uri.getPath))
+        case null | "file" =>
+            if (!isYarn)
+                env.httpFileServer.addJar(new File(uri.getPath))
+            else
+                null
         case _ => path
       }
-      addedJars(key) = System.currentTimeMillis
-      logInfo("Added JAR " + path + " at " + key + " with timestamp " + addedJars(key))
+
+      if (key != null) {
+        addedJars(key) = System.currentTimeMillis
+        logInfo("Added JAR " + path + " at " + key + " with timestamp " + addedJars(key))
+      }
     }
   }