PG-186: Add support to monitor query execution plan.

Fix a regression test case.

regression/expected/user.out

@@ -1,5 +1,5 @@
-DROP USER IF EXISTS su;
 CREATE USER su WITH SUPERUSER;
+ERROR:  role "su" already exists
 SET ROLE su;
 CREATE EXTENSION pg_stat_monitor;
 CREATE USER u1;

regression/sql/user.sql

@@ -1,4 +1,3 @@
-DROP USER IF EXISTS su;
 CREATE USER su WITH SUPERUSER;
 
 SET ROLE su;