automatically set master according to `spark.master` in `spark-defaults....

automatically set master according to `spark.master` in `spark-defaults.conf`

Author: CrazyJvm <crazyjvm@gmail.com>

Closes #1644 from CrazyJvm/standalone-guide and squashes the following commits:

bb12b95 [CrazyJvm] automatically set master according to `spark.master` in `spark-defaults.conf`