IMPALA-1248: Fixed CHAR(N) in VALUES clause.

Queries like;
INSERT INTO table VALUES (CAST("..." AS CHAR(N)))
Used codegen path and failed; changed to use interpreted path.

Change-Id: Id80274580df268b3f828dec19a2e0b0578061ca8
Reviewed-on: http://gerrit.sjc.cloudera.com:8080/4362
Reviewed-by: Victor Bittorf <victor.bittorf@cloudera.com>
Tested-by: jenkins