Preprocessing step for Spark history file processing

Enables the preprocessing step to process Spark history/conf files.

Ensures the "spark" prefix is applied to spark jobs, but backwards compatibility is maintained for hadoop jobs. hRaven till now presumed the prefix to be "job" for all job ids. All the JobIds, JobKeys, Row keys did not contain this prefix , but now we need to add existence of such a prefix to include spark files.

Given that JobId never has prefix = JOB_PREFIX, can't we remove the latter check?