SPARK-4567. Make SparkJobInfo and SparkStageInfo serializable

Author: Sandy Ryza <sandy@cloudera.com>

Closes #3426 from sryza/sandy-spark-4567 and squashes the following commits:

cb4b8d2 [Sandy Ryza] SPARK-4567. Make SparkJobInfo and SparkStageInfo serializable

(cherry picked from commit 5e4c06f8e54265a4024857f5978ec54c936aeea2)
Signed-off-by: Josh Rosen <joshrosen@databricks.com>