[SPARK-9737] [YARN] Add the suggested configuration when required executor...

[SPARK-9737] [YARN] Add the suggested configuration when required executor memory is above the max threshold of this cluster on YARN mode

Author: Yadong Qi <qiyadong2010@gmail.com>

Closes #8028 from watermen/SPARK-9737 and squashes the following commits:

48bdf3d [Yadong Qi] Add suggested configuration.