kiji-rest: REST-84. kiji-rest script should allow specifying JVM arguments.

 - Introduce KIJI_REST_JAVA_ARGUMENTS for users to specify JVM arguments.

issue: https://jira.kiji.org/browse/REST-84
review: https://review.kiji.org/r/1488
commit: https://github.com/kijiproject/kiji-rest/commit/a278dadd9fca233365b24f20a2f06e42ec4947e6