kiji-schema-shell: DDLSHELL-55. alter table set validation = ... does not work

issue: https://jira.kiji.org/browse/DDLSHELL-55
review: https://review.kiji.org/r/1595
commit: https://github.com/kijiproject/kiji-schema-shell/commit/b34540f4a11a9e83cd6165500516d1b6383b6d1f