kiji-scoring: SCORE-181. Determine how we can encode the per-request parameters in the model_container

issue: https://jira.kiji.org/browse/SCORE-181
review: https://review.kiji.org/r/1883
commit: https://github.com/kijiproject/kiji-scoring/commit/5d166915fecf9eee48a44a3b115d0bc81bf654b2