update minAllowedPort of gpaddmirrors
update minAllowedPort of gpaddmirrors

Because the default offset is 1000, the default min port is 5432
（primary port + offset = mirror database port）
so， the default minAllowedPort should be 6432

minPort = min([seg.getSegmentPort() for seg in gpArray.getDbList()])
50wu/gpdb,greenplum-db/gpdb,greenplum-db/gpdb,greenplum-db/gpdb,adam8157/gpdb,ashwinstar/gpdb,xinzweb/gpdb,xinzweb/gpdb,xinzweb/gpdb,xinzweb/gpdb,lisakowen/gpdb,jmcatamney/gpdb,ashwinstar/gpdb,jmcatamney/gpdb,ashwinstar/gpdb,jmcatamney/gpdb,greenplum-db/gpdb,50wu/gpdb,jmcatamney/gpdb,xinzweb/gpdb,lisakowen/gpdb,50wu/gpdb,greenplum-db/gpdb,ashwinstar/gpdb,lisakowen/gpdb,lisakowen/gpdb,50wu/gpdb,ashwinstar/gpdb,greenplum-db/gpdb,lisakowen/gpdb,xinzweb/gpdb,greenplum-db/gpdb,lisakowen/gpdb,50wu/gpdb,ashwinstar/gpdb,ashwinstar/gpdb,50wu/gpdb,jmcatamney/gpdb,adam8157/gpdb,lisakowen/gpdb,lisakowen/gpdb,adam8157/gpdb,adam8157/gpdb,50wu/gpdb,xinzweb/gpdb,jmcatamney/gpdb,50wu/gpdb,ashwinstar/gpdb,jmcatamney/gpdb,greenplum-db/gpdb,jmcatamney/gpdb,adam8157/gpdb,xinzweb/gpdb,adam8157/gpdb,adam8157/gpdb,adam8157/gpdb