MDEV-35617: DROP USER should leave no active session for that user

DROP USER looks for sessions by the do-be-dropped user and if found:
* fails with ER_CANNOT_USER in Oracle mode
* continues with ER_ACTIVE_CONNECTIONS_FOR_USER_TO_DROP warning otherwise

Every user being dropped is marked with flag that disallow establishing
a new connections on behalf this user.

mysql-test/suite/rpl/r/rpl_password_boundaries.result

@@ -54,6 +54,8 @@ ERROR HY000: String 'воттакойужпарольвоттакойужпар
 connection master;
 set sql_log_bin=0;
 drop user rpl32@127.0.0.1, rpl33@127.0.0.1, rpl16cyr@127.0.0.1, rpl17mix@127.0.0.1;
+Warnings:
+Note	4227	Dropped users 'rpl16cyr'@'127.0.0.1' have active connections. Use KILL CONNECTION if they should not be used anymore.
 set sql_log_bin=1;
 connection slave;
 change master to master_user='root',master_password='';

mysql-test/suite/rpl/r/rpl_perfschema_connect_config.result

@@ -57,6 +57,8 @@ include/assert.inc [Value returned by SSS and PS table for SSL_Key should be sam
 include/assert.inc [Value returned by SSS and PS table for SSL_Verify_Server_Certificate should be same.]
 connection master;
 drop user replssl@localhost;
+Warnings:
+Note	4227	Dropped users 'replssl'@'localhost' have active connections. Use KILL CONNECTION if they should not be used anymore.
 connection slave;
 include/stop_slave.inc
 CHANGE MASTER TO

mysql-test/suite/rpl/r/rpl_slave_alias_replica.result

@@ -22,6 +22,8 @@ connection slave;
 connection master;
 "Command: SHOW SLAVE HOSTS --> SHOW REPLICA HOSTS"
 DROP USER 'repl_user';
+Warnings:
+Note	4227	Dropped users 'repl_user'@'%' have active connections. Use KILL CONNECTION if they should not be used anymore.
 connection slave;
 "Command: SHOW SLAVE IO/SQL THREAD --> SHOW REPLICA IO/SQL THREAD"
 STOP REPLICA IO_THREAD;

mysql-test/suite/rpl/r/rpl_slave_restart_long_password.result

@@ -18,6 +18,8 @@ include/check_slave_param.inc [Slave_IO_Running]
 connection master;
 SET SQL_LOG_BIN=0;
 DROP USER rpl@127.0.0.1;
+Warnings:
+Note	4227	Dropped users 'rpl'@'127.0.0.1' have active connections. Use KILL CONNECTION if they should not be used anymore.
 FLUSH PRIVILEGES;
 SET SQL_LOG_BIN=1;
 connection slave;

mysql-test/suite/rpl/r/rpl_slave_status.result

@@ -30,6 +30,8 @@ n
 ==== Delete new replication user ====
 connection master;
 DROP USER rpl@127.0.0.1;
+Warnings:
+Note	4227	Dropped users 'rpl'@'127.0.0.1' have active connections. Use KILL CONNECTION if they should not be used anymore.
 FLUSH PRIVILEGES;
 connection slave;
 ==== Restart slave without privileges =====

mysql-test/suite/rpl/r/rpl_ssl.result

@@ -46,6 +46,8 @@ Master_SSL_Key = 'MYSQL_TEST_DIR/std_data/client-key.pem'
 include/check_slave_is_running.inc
 connection master;
 drop user replssl@localhost;
+Warnings:
+Note	4227	Dropped users 'replssl'@'localhost' have active connections. Use KILL CONNECTION if they should not be used anymore.
 drop table t1;
 connection slave;
 include/stop_slave.inc
@@ -55,5 +57,5 @@ master_ssl = 1,
 master_ssl_ca = '',
 master_ssl_cert = '',
 master_ssl_key = '';
-End of 5.0 tests
+# End of 5.0 tests
 include/rpl_end.inc

mysql-test/suite/rpl/r/rpl_ssl1.result

@@ -112,6 +112,8 @@ master_ssl_verify_server_cert=0,
 master_ssl=1;
 connection master;
 drop user replssl@127.0.0.1;
+Warnings:
+Note	4227	Dropped users 'replssl'@'127.0.0.1' have active connections. Use KILL CONNECTION if they should not be used anymore.
 connection slave;
 drop user replssl@127.0.0.1;
 include/rpl_end.inc

mysql-test/suite/rpl/t/rpl_ssl1.test

@@ -61,7 +61,9 @@ change master to master_user='root',master_password='', master_ssl=0;
 start slave;
 --source include/wait_for_slave_to_start.inc
 connection master;
+disable_warnings;
 drop user replssl@localhost;
+enable_warnings;
 drop table t1;
 
 sync_slave_with_master;