[SPARK-2109] Setting SPARK_MEM for bin/pyspark does not work.

Trivial fix.

Author: Prashant Sharma <prashant.s@imaginea.com>

Closes #1050 from ScrapCodes/SPARK-2109/pyspark-script-bug and squashes the following commits:

77072b9 [Prashant Sharma] Changed echos to redirect to STDERR.
13f48a0 [Prashant Sharma] [SPARK-2109] Setting SPARK_MEM for bin/pyspark does not work.
(cherry picked from commit 731f683b1bd8abbb83030b6bae14876658bbf098)

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