Now that pg_upgrade uses -w in pg_ctl, remove loop that retried testing

the connection;  also restructure the libpq connection code.

This patch also removes the unused variable postmasterPID and fixes a
libpq structure leak that was in the testing loop.

contrib/pg_upgrade/pg_upgrade.h

@@ -227,7 +227,6 @@ typedef struct
 	int			num_tablespaces;
 	char	  **libraries;		/* loadable libraries */
 	int			num_libraries;
-	pgpid_t		postmasterPID;	/* PID of currently running postmaster */
 	ClusterInfo *running_cluster;
 } OSInfo;