[SPARK-11880][WINDOWS][SPARK SUBMIT] bin/load-spark-env.cmd loads spark-env.cmd from wrong directory

* On windows the `bin/load-spark-env.cmd` tries to load `spark-env.cmd` from `%~dp0..\..\conf`, where `~dp0` points to `bin` and `conf` is only one level up.
* Updated `bin/load-spark-env.cmd` to load `spark-env.cmd` from `%~dp0..\conf`, instead of `%~dp0..\..\conf`

Author: wangt <wangtao.upc@gmail.com>

Closes #9863 from toddwan/master.