REST-118. Ensure that KijiREST starts if ZK has old Kiji instances.

If ZK has Outdated metadata in ZK which was not updated properly when instances
were remove, KijiREST wouldn't start up. Now those errors are just
logged but KijiREST continues to boot.

Review: https://review.kiji.org/r/1764/
Reviewer: shashir, dan