SPARK-2181:The keys for sorting the columns of Executor page in SparkUI are incorrect

Author: witgo <witgo@qq.com>

Closes #1135 from witgo/SPARK-2181 and squashes the following commits:

39dad90 [witgo] The keys for sorting the columns of Executor page in SparkUI are incorrect
(cherry picked from commit 18f29b96c7e0948f5f504e522e5aa8a8d1ab163e)

Signed-off-by: Patrick Wendell <pwendell@gmail.com>