pg_upgrade: Fix fatal error handling
pg_upgrade: Fix fatal error handling

Restore exiting when pg_log(PG_FATAL) is called directly instead of
calling pg_fatal().  Fault introduced in
264aa14a2f687eba8c8cc2a5b6cbd6397973da98.

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