MDEV-22513 main.processlist_notembedded Timeout in wait_until_count_sessions

Do not blindly disconnect the connection that is in WAIT_FOR
because it could happen that neither the disconnect nor the
SIGNAL would be processed before RESET would discard the signal.

mysql-test/r/processlist_notembedded.result

@@ -4,5 +4,6 @@
 SET DEBUG_SYNC= 'before_join_optimize SIGNAL in_sync WAIT_FOR go';
 SET DEBUG_SYNC= 'now WAIT_FOR in_sync';
 SET DEBUG_SYNC= 'now SIGNAL go';
+user
 SET DEBUG_SYNC = 'RESET';
 End of 5.5 tests

mysql-test/t/processlist_notembedded.test

@@ -30,7 +30,10 @@ remove_file $MYSQLTEST_VARDIR/tmp//MDEV-20466.text;
 
 SET DEBUG_SYNC= 'now SIGNAL go';
 
+connection con1;
+reap;
 disconnect con1;
+connection default;
 
 SET DEBUG_SYNC = 'RESET';