Add a targeted test that confirms that setting the query option will
force spilling.
Testing:
Ran test_spilling locally.
Change-Id: Ida6b55b2dee0779b1739af5d75943518ec40d6ce
Reviewed-on: http://gerrit.cloudera.org:8080/7809
Reviewed-by: Tim Armstrong <tarmstrong@cloudera.com>
Tested-by: Impala Public Jenkins
