kiji-schema-shell: DDLSHELL-61. Allow Avro DSL in DDL statements.

 - Add simple unit-test.

issue: https://jira.kiji.org/browse/DDLSHELL-61
review: https://review.kiji.org/r/1570
commit: https://github.com/kijiproject/kiji-schema-shell/commit/e95a279b526465d2ae25fb3db8339d18c53666ad