[SPARK-22788][STREAMING] Use correct hadoop config for fs append supp…

…ort.

Still look at the old one in case any Spark user is setting it
explicitly, though.

Author: Marcelo Vanzin <vanzin@cloudera.com>

Closes #19983 from vanzin/SPARK-22788.

streaming/src/main/scala/org/apache/spark/streaming/util/HdfsUtils.scala

@@ -29,7 +29,9 @@ private[streaming] object HdfsUtils {
     // If the file exists and we have append support, append instead of creating a new file
     val stream: FSDataOutputStream = {
       if (dfs.isFile(dfsPath)) {
-        if (conf.getBoolean("hdfs.append.support", false) || dfs.isInstanceOf[RawLocalFileSystem]) {
+        if (conf.getBoolean("dfs.support.append", true) ||
+            conf.getBoolean("hdfs.append.support", false) ||
+            dfs.isInstanceOf[RawLocalFileSystem]) {
           dfs.append(dfsPath)
         } else {
           throw new IllegalStateException("File exists and there is no append support!")