kiji-scoring: SCORE-152. TableReadCallable should be constructed from a reader pool instead of a reader

issue: https://jira.kiji.org/browse/SCORE-152
review: https://review.kiji.org/r/1611
commit: https://github.com/kijiproject/kiji-scoring/commit/ea29b8c20c610b3512d2f473e8a8553b0c65a706