kiji-bento: BENTO-95. Configure repositories to explicitly specify whether they contain snapshots.

issue: https://jira.kiji.org/browse/BENTO-95
review: https://review.kiji.org/r/1994
commit: https://github.com/kijiproject/kiji-bento/commit/c14002e4691dc8079a752a24e83aedcfdbab70e2