Fix config and add tests for Broadcast

1. fix the pyspark tests in config.py.template
2. add a option to disable rsync SPARK_HOME
3. add two tests for python broadcast
4. dump the configs and results as json
5. some refactor
6. add --list and --al

Author: Davies Liu <davies@databricks.com>
Author: Davies Liu <davies.liu@gmail.com>

Closes #28 from davies/json and squashes the following commits:

71ebc9b [Davies Liu] add --list and --all
5773ecb [Davies Liu] cleanup
3641ce1 [Davies Liu] fix config
a244e6c [Davies Liu] Merge branch 'master' of https://github.com/databricks/spark-perf into broadcast
def130a [Davies Liu] add test for broadcast