HDFS-6951. Correctly persist raw namespace xattrs to edit log and fsimage. Contributed by Charles Lamb.

(cherry picked from commit 04915a08141bbe71bdef26e3f539aa8b76f89ac7)
Update CHANGES.txt for HDFS-6951

(cherry picked from commit 7498dd790eca39c142229a75c2801b5bf4b94983)