Add test for backslashes.

Author: Marcelo Vanzin

yarn/common/src/test/scala/org/apache/spark/deploy/yarn/YarnSparkHadoopUtilSuite.scala

@@ -44,7 +44,7 @@ class YarnSparkHadoopUtilSuite extends FunSuite with Matchers with Logging {
 
   bashTest("shell script escaping") {
     val scriptFile = File.createTempFile("script.", ".sh")
-    val args = Array("arg1", "${arg.2}", "\"arg3\"", "'arg4'", "$arg5")
+    val args = Array("arg1", "${arg.2}", "\"arg3\"", "'arg4'", "$arg5", "\\arg6")
     try {
       val argLine = args.map(a => YarnSparkHadoopUtil.escapeForShell(a)).mkString(" ")
       Files.write(("bash -c \"echo " + argLine + "\"").getBytes(), scriptFile)