kiji-schema: SCHEMA-365. Improve Invalid family name error message in KijiColumnName.validateNames

issue: https://jira.kiji.org/browse/SCHEMA-365
review: https://review.kiji.org/r/1583
commit: https://github.com/kijiproject/kiji-schema/commit/5719cb273f7a9db4ddb2d0f428d596eede703ab2