pg_upgrade:  call 'postgres' binary to get data directory location
pg_upgrade:  call 'postgres' binary to get data directory location

This matches the binary 'pg_ctl' calls.  Previously we called the
'postmaster'.

Report by Christoph Berg

oberstet/postgres-xl,50wu/gpdb,jmcatamney/gpdb,xinzweb/gpdb,50wu/gpdb,adam8157/gpdb,adam8157/gpdb,yazun/postgres-xl,ovr/postgres-xl,adam8157/gpdb,jmcatamney/gpdb,xinzweb/gpdb,xinzweb/gpdb,ovr/postgres-xl,techdragon/Postgres-XL,ashwinstar/gpdb,jmcatamney/gpdb,50wu/gpdb,Postgres-XL/Postgres-XL,lisakowen/gpdb,Postgres-XL/Postgres-XL,yazun/postgres-xl,lisakowen/gpdb,50wu/gpdb,greenplum-db/gpdb,zeroae/postgres-xl,zeroae/postgres-xl,zeroae/postgres-xl,Postgres-XL/Postgres-XL,Postgres-XL/Postgres-XL,jmcatamney/gpdb,oberstet/postgres-xl,xinzweb/gpdb,lisakowen/gpdb,lisakowen/gpdb,50wu/gpdb,lisakowen/gpdb,ovr/postgres-xl,zeroae/postgres-xl,pavanvd/postgres-xl,jmcatamney/gpdb,oberstet/postgres-xl,ashwinstar/gpdb,greenplum-db/gpdb,zeroae/postgres-xl,greenplum-db/gpdb,xinzweb/gpdb,50wu/gpdb,jmcatamney/gpdb,ashwinstar/gpdb,techdragon/Postgres-XL,pavanvd/postgres-xl,greenplum-db/gpdb,adam8157/gpdb,jmcatamney/gpdb,50wu/gpdb,lisakowen/gpdb,jmcatamney/gpdb,ovr/postgres-xl,xinzweb/gpdb,adam8157/gpdb,yazun/postgres-xl,greenplum-db/gpdb,ashwinstar/gpdb,ashwinstar/gpdb,xinzweb/gpdb,adam8157/gpdb,greenplum-db/gpdb,ovr/postgres-xl,yazun/postgres-xl,greenplum-db/gpdb,lisakowen/gpdb,ashwinstar/gpdb,techdragon/Postgres-XL,oberstet/postgres-xl,ashwinstar/gpdb,adam8157/gpdb,greenplum-db/gpdb,techdragon/Postgres-XL,pavanvd/postgres-xl,lisakowen/gpdb,pavanvd/postgres-xl,xinzweb/gpdb,pavanvd/postgres-xl,adam8157/gpdb,yazun/postgres-xl,Postgres-XL/Postgres-XL,50wu/gpdb,oberstet/postgres-xl,ashwinstar/gpdb,techdragon/Postgres-XL