MDEV-36835 - main.aborted_clients fails after various tests

Some tests like main.ssl_timeout and main.wait_timeout may abort
connections. If main.aborted_clients follows such tests it may
observe unstable value of aborted_clients status variable.

FLUSH STATUS was issued to make aborted_clients value reproducible.
However after 775cba4 FLUSH STATUS doesn't reset global status.

Fixed by using FLUSH GLOBAL STATUS.

Regression after "MDEV-33145 - Add FLUSH GLOBAL STATUS".

Author: svoj

mysql-test/main/aborted_clients.result

@@ -1,4 +1,4 @@
-FLUSH STATUS;
+FLUSH GLOBAL STATUS;
 connect  con1,localhost,root,,;
 disconnect con1;
 connection default;

mysql-test/main/aborted_clients.test

@@ -5,7 +5,7 @@
 -- source include/not_embedded.inc
 -- source include/count_sessions.inc
 
-FLUSH STATUS;
+FLUSH GLOBAL STATUS;
 # Connect/Disconnect look that aborted_clients stays 0
 connect (con1,localhost,root,,);
 disconnect con1;