kiji-schema: SCHEMA-614. Fix issue where Kiji metadata backup isn't backing up all versions of the metadata.

issue: https://jira.kiji.org/browse/SCHEMA-614
review: https://review.kiji.org/r/2063
commit: https://github.com/kijiproject/kiji-schema/commit/15bb4e712cd82927e649120d55e85b4c8741ff24