isolation2: add a master-and-primary utility command
isolation2: add a master-and-primary utility command

The '*U:' command flag will connect to the master and all primaries to
execute its query. The intended use case is for easy testing of
distributed catalog changes.

greenplum-db/gpdb,lisakowen/gpdb,adam8157/gpdb,ashwinstar/gpdb,jmcatamney/gpdb,xinzweb/gpdb,xinzweb/gpdb,lisakowen/gpdb,ashwinstar/gpdb,50wu/gpdb,greenplum-db/gpdb,xinzweb/gpdb,lisakowen/gpdb,adam8157/gpdb,50wu/gpdb,50wu/gpdb,ashwinstar/gpdb,greenplum-db/gpdb,ashwinstar/gpdb,jmcatamney/gpdb,lisakowen/gpdb,ashwinstar/gpdb,lisakowen/gpdb,adam8157/gpdb,adam8157/gpdb,greenplum-db/gpdb,jmcatamney/gpdb,50wu/gpdb,ashwinstar/gpdb,jmcatamney/gpdb,adam8157/gpdb,greenplum-db/gpdb,greenplum-db/gpdb,50wu/gpdb,50wu/gpdb,lisakowen/gpdb,lisakowen/gpdb,jmcatamney/gpdb,50wu/gpdb,adam8157/gpdb,greenplum-db/gpdb,xinzweb/gpdb,ashwinstar/gpdb,xinzweb/gpdb,xinzweb/gpdb,jmcatamney/gpdb,xinzweb/gpdb,lisakowen/gpdb,adam8157/gpdb,ashwinstar/gpdb,50wu/gpdb,greenplum-db/gpdb,jmcatamney/gpdb,adam8157/gpdb,jmcatamney/gpdb,xinzweb/gpdb