kiji-rest: REST-63. KijiREST should have a mode to serve all Kiji instances in a cluster.

issue: https://jira.kiji.org/browse/REST-63
review: https://review.kiji.org/r/1486
commit: https://github.com/kijiproject/kiji-rest/commit/0bb66e9c634bdb71379ef3468b3781b19f17ab77