kiji-modeling: EXP-284. Relax access modifier for the KeyValueStores#keyValueStores setter.

issue: https://jira.kiji.org/browse/EXP-284
review: https://review.kiji.org/r/1335
commit: https://github.com/kijiproject/kiji-modeling/commit/fd81e862bdf9f031b78687a9d3b3acae1144b7df