Refactor test_gpdb.py for different modes (#3901)
Refactor test_gpdb.py for different modes (#3901)

- Handle missing case for codegen mode

Signed-off-by: Larry Hamel <c5a53acaa5da6b424e2bd28a0587d04439c72a22@pivotal.io>
ashwinstar/gpdb,greenplum-db/gpdb,Chibin/gpdb,edespino/gpdb,edespino/gpdb,ashwinstar/gpdb,edespino/gpdb,50wu/gpdb,jmcatamney/gpdb,xinzweb/gpdb,yuanzhao/gpdb,xinzweb/gpdb,jmcatamney/gpdb,yuanzhao/gpdb,yuanzhao/gpdb,adam8157/gpdb,50wu/gpdb,ashwinstar/gpdb,yuanzhao/gpdb,jmcatamney/gpdb,50wu/gpdb,lisakowen/gpdb,ashwinstar/gpdb,adam8157/gpdb,lisakowen/gpdb,adam8157/gpdb,jmcatamney/gpdb,edespino/gpdb,edespino/gpdb,adam8157/gpdb,greenplum-db/gpdb,edespino/gpdb,greenplum-db/gpdb,edespino/gpdb,50wu/gpdb,greenplum-db/gpdb,lisakowen/gpdb,Chibin/gpdb,greenplum-db/gpdb,ashwinstar/gpdb,xinzweb/gpdb,xinzweb/gpdb,lisakowen/gpdb,edespino/gpdb,yuanzhao/gpdb,xinzweb/gpdb,Chibin/gpdb,lisakowen/gpdb,xinzweb/gpdb,jmcatamney/gpdb,lisakowen/gpdb,50wu/gpdb,50wu/gpdb,Chibin/gpdb,adam8157/gpdb,lisakowen/gpdb,yuanzhao/gpdb,50wu/gpdb,ashwinstar/gpdb,lisakowen/gpdb,yuanzhao/gpdb,adam8157/gpdb,xinzweb/gpdb,greenplum-db/gpdb,jmcatamney/gpdb,edespino/gpdb,adam8157/gpdb,edespino/gpdb,greenplum-db/gpdb,50wu/gpdb,yuanzhao/gpdb,Chibin/gpdb,yuanzhao/gpdb,ashwinstar/gpdb,greenplum-db/gpdb,jmcatamney/gpdb,ashwinstar/gpdb,Chibin/gpdb,jmcatamney/gpdb,Chibin/gpdb,Chibin/gpdb,Chibin/gpdb,yuanzhao/gpdb,adam8157/gpdb,Chibin/gpdb,xinzweb/gpdb