Disable JobGeneratorSuite "Do not clear received block data too soon".

streaming/src/test/scala/org/apache/spark/streaming/scheduler/JobGeneratorSuite.scala

@@ -56,7 +56,8 @@ class JobGeneratorSuite extends TestSuiteBase {
   // 4. allow subsequent batches to be generated (to allow premature deletion of 3rd batch metadata)
   // 5. verify whether 3rd batch's block metadata still exists
   //
-  test("SPARK-6222: Do not clear received block data too soon") {
+  // TODO: SPARK-7420 enable this test
+  ignore("SPARK-6222: Do not clear received block data too soon") {
     import JobGeneratorSuite._
     val checkpointDir = Utils.createTempDir()
     val testConf = conf