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
SPARK-4805 [CORE] BlockTransferMessage.toByteArray() trips assertion

Allocate enough room for type byte as well as message, to avoid tripping assertion about capacity of the buffer

Author: Sean Owen <sowen@cloudera.com>

Closes #3650 from srowen/SPARK-4805 and squashes the following commits:

9e1d502 [Sean Owen] Allocate enough room for type byte as well as message, to avoid tripping assertion about capacity of the buffer