Spark history file processing

Enables the preprocessing, rawloader and processing steps 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.

Adds SparkJobDescFactory, JobHistoryFileParserSpark classes

If the processing step is going to be run on a hadoop1 cluster, then jackson-1.8.8 libraries need to occur in the classpath before the jackson-1.5.2 libraries . The jackson 1.5.2 libraries come with hadoop. 
Hence we need set -Dmapreduce.task.classpath.user.precedence=true parameter at the processing step and add $(ls /usr/local/hbase/lib/jackson-core-asl-*.jar),$(ls /usr/local/hbase/lib/jackson-mapper-asl-*.jar) to the libjars at the processing step for hadoop1 clusters.

Out of curiosity, how is this number (21) derived?