Cherry-pick of 'mariadb-test: wait on disconnect' from 12.1

Cherry-picks mysqltest.cc and rpl_semi_sync_shutdown_await_ack changes
from 12.1 to fix a race condition on disconnect.

Author: DaveGosselin-MariaDB

client/mysqltest.cc

@@ -5767,8 +5767,12 @@ void do_close_connection(struct st_command *command)
   DBUG_PRINT("info", ("Closing connection %s", con->name));
 #ifndef EMBEDDED_LIBRARY
   if (command->type == Q_DIRTY_CLOSE)
-  {
     mariadb_cancel(con->mysql);
+  else
+  {
+    simple_command(con->mysql,COM_QUIT,0,0,0);
+    if (con->util_mysql)
+      simple_command(con->util_mysql,COM_QUIT,0,0,0);
   }
 #endif /*!EMBEDDED_LIBRARY*/
   if (con->stmt)

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

@@ -219,7 +219,7 @@ SET GLOBAL debug_dbug="+d,simulate_delay_semisync_slave_reply";
 --connection server_2
 set debug_sync= "now wait_for io_thd_at_slave_reply";
 
---disconnect con1
+--dirty_close con1
 
 --connection default
 --write_file $MYSQLTEST_VARDIR/tmp/mysqld.1.expect