[CDH5] Sanity Tests for decimal.

This patch adds a test that checks whether we are able to properly cast a value to a
Decimal type.

Change-Id: I8b66dc1c0e4b67e5d5a7cbae738682bf392964c8
Reviewed-on: http://gerrit.sjc.cloudera.com:8080/2831
Reviewed-by: Ishaan Joshi <ishaan@cloudera.com>
Tested-by: jenkins