[SPARK-4415] [PySpark] JVM should exit after Python exit

When JVM is started in a Python process, it should exit once the stdin is closed.

test: add spark.driver.memory in conf/spark-defaults.conf

```
daviesdm:~/work/spark$ cat conf/spark-defaults.conf
spark.driver.memory       8g
daviesdm:~/work/spark$ bin/pyspark
>>> quit
daviesdm:~/work/spark$ jps
4931 Jps
286
daviesdm:~/work/spark$ python wc.py
943738
0.719928026199
daviesdm:~/work/spark$ jps
286
4990 Jps
```

Author: Davies Liu <davies@databricks.com>

Closes #3274 from davies/exit and squashes the following commits:

df0e524 [Davies Liu] address comments
ce8599c [Davies Liu] address comments
050651f [Davies Liu] JVM should exit after Python exit

1 files changed, 0 insertions, 2 deletions

diff --git a/bin/pyspark b/bin/pyspark
index 1d8c94d43d..0b4f695dd0 100755
--- a/bin/pyspark
+++ b/bin/pyspark
@@ -132,7 +132,5 @@ if [[ "$1" =~ \.py$ ]]; then
   gatherSparkSubmitOpts "$@"
   exec "$FWDIR"/bin/spark-submit "${SUBMISSION_OPTS[@]}" "$primary" "${APPLICATION_OPTS[@]}"
 else
-  # PySpark shell requires special handling downstream
-  export PYSPARK_SHELL=1
   exec "$PYSPARK_DRIVER_PYTHON" $PYSPARK_DRIVER_PYTHON_OPTS
 fi