Update GPORCA concourse pipeline [#117366937]
Update GPORCA concourse pipeline [#117366937]

Created a new group called 'gpdb' to narrow down pipeline.

Reduce trigger of build_gpdb_centos6 and gpdb_icg to only
be trigered by a successful orca_centos6_release build.

Add trigger of orca_centos6_release with new gp_xerces build.

Reduced worker of GPDB_ICG into 1. The reason to reduce the
worker to 1 is 'gpdb_icg' tests are very heavy, and they
don't work well with multiple of them to run, especially
when they share same worker in different containers.

Furthermore, concourse UI got wrong log output when there are more
than 1 builds going on, and ICG test output got duplicated.

PengJi/gporca-comments,xinzweb/gpdb,lisakowen/gpdb,adam8157/gpdb,greenplum-db/gpdb,xinzweb/gpdb,adam8157/gpdb,xinzweb/gpdb,adam8157/gpdb,xinzweb/gpdb,50wu/gpdb,jmcatamney/gpdb,jmcatamney/gpdb,lisakowen/gpdb,50wu/gpdb,adam8157/gpdb,adam8157/gpdb,lisakowen/gpdb,greenplum-db/gpdb,adam8157/gpdb,lisakowen/gpdb,greenplum-db/gpdb,greenplum-db/gporca,lisakowen/gpdb,greenplum-db/gporca,adam8157/gpdb,xinzweb/gpdb,greenplum-db/gporca,PengJi/gporca-comments,50wu/gpdb,greenplum-db/gpdb,xinzweb/gpdb,50wu/gpdb,greenplum-db/gpdb,xinzweb/gpdb,PengJi/gporca-comments,PengJi/gporca-comments,50wu/gpdb,greenplum-db/gporca,lisakowen/gpdb,50wu/gpdb,jmcatamney/gpdb,greenplum-db/gpdb,50wu/gpdb,greenplum-db/gpdb,jmcatamney/gpdb,adam8157/gpdb,greenplum-db/gpdb,lisakowen/gpdb,lisakowen/gpdb,50wu/gpdb,jmcatamney/gpdb,jmcatamney/gpdb,PengJi/gporca-comments,jmcatamney/gpdb,xinzweb/gpdb,jmcatamney/gpdb