[CDH4] IMPALA-1501: Error during small query optimization for joins

Small query optimization cannot be applied for join queries as two scans
cannot be executed concurrently in a single fragment.

Change-Id: I1ebe5ff2496bf83cdccdc450584d6e1826766095
Reviewed-on: http://gerrit.sjc.cloudera.com:8080/5350
Reviewed-by: Alex Behm <alex.behm@cloudera.com>
Tested-by: jenkins