kiji-scoring: SCORE-159. ScoringServerScoreFunction should read the server baseURI from a system table

issue: https://jira.kiji.org/browse/SCORE-159
review: https://review.kiji.org/r/1659
commit: https://github.com/kijiproject/kiji-scoring/commit/ef85b8776bed0e65af7fc91e67f740c2f35dabb4