kiji-scoring: SCORE-157. Update ScoringServerScoreFunction to the new ScoringServer APIs.

issue: https://jira.kiji.org/browse/SCORE-157
review: https://review.kiji.org/r/1653
commit: https://github.com/kijiproject/kiji-scoring/commit/01f9da8ff29f48163d75a50730420485835b0df7