delete no use var

Author: wangfei <wangfei_hello@126.com>

Closes #613 from scwf/masterIndex and squashes the following commits:

1463056 [wangfei] delete no use var: masterIndex
SPARK-1492. Update Spark YARN docs to use spark-submit

Author: Sandy Ryza <sandy@cloudera.com>

Closes #601 from sryza/sandy-spark-1492 and squashes the following commits:

5df1634 [Sandy Ryza] Address additional comments from Patrick.
be46d1f [Sandy Ryza] Address feedback from Marcelo and Patrick
867a3ea [Sandy Ryza] SPARK-1492. Update Spark YARN docs to use spark-submit
SPARK-1700: Close socket file descriptors on task completion

This will ensure that sockets do not build up over the course of a job, and that cancellation successfully cleans up sockets.

Tested in standalone mode. More file descriptors spawn than expected (around 1000ish rather than the expected 8ish) but they do not pile up between runs, or as high as before (where they went up to around 5k).

Author: Aaron Davidson <aaron@databricks.com>

Closes #623 from aarondav/pyspark2 and squashes the following commits:

0ca13bb [Aaron Davidson] SPARK-1700: Close socket file descriptors on task completion
Update SchemaRDD.scala

Modify spelling errors

Author: ArcherShao <ArcherShao@users.noreply.github.com>

Closes #619 from ArcherShao/patch-1 and squashes the following commits:

2957195 [ArcherShao] Update SchemaRDD.scala