kiji-schema-shell: DDLSHELL-63. DDL shell must return exit code ≠ 0 if DDL cannot be applied or if Avro class cannot be found.

issue: https://jira.kiji.org/browse/DDLSHELL-63
review: https://review.kiji.org/r/1594
commit: https://github.com/kijiproject/kiji-schema-shell/commit/46483a1b5651f38f3071717a19670b10eab124c2