CDAP-713: Updated SparkPageRank archetype according to migration from procedures to services.
Merge remote-tracking branch 'upstream/release/2.6.0' into CDAP-713/SparkPageRank-example-archetype-2.6.0
CDAP-713: Updated docs.
Merge pull request #703 from cybervisiontech/CDAP-713/SparkPageRank-example-archetype-2.6.0

CDAP-713: Updated SparkPageRank archetype according to migration to services.