kiji-schema: SCHEMA-591. Plug ColumnReaderSpec in KijiDataRequest.

issue: https://jira.kiji.org/browse/SCHEMA-591
review: https://review.kiji.org/r/1255
commit: https://github.com/kijiproject/kiji-schema/commit/622798a36bd3db8f450f7c23e46fc924ae744727