Limit test_udfs to always run with a single exec_option test vector

Change-Id: If3ff1f5f17a95cce88282f9dc165fe5ce85200b9
Reviewed-on: http://gerrit.ent.cloudera.com:8080/1781
Reviewed-by: Alex Behm <alex.behm@cloudera.com>
Tested-by: jenkins