Fixed ya main.flush_read_lock sporadic failure

Use different signal names, so that subsequent WAIT_FOR is not awaken by
previous signal.

mysql-test/main/flush_read_lock.result

@@ -1741,14 +1741,14 @@ CREATE DATABASE mysqltest;
 CREATE TABLE mysqltest.t1(a INT);
 HANDLER mysqltest.t1 OPEN as t1;
 connect  con1,localhost,root,,;
-SET DEBUG_SYNC= 'mdl_acquire_lock_wait SIGNAL ready';
+SET DEBUG_SYNC= 'mdl_acquire_lock_wait SIGNAL ready1';
 LOCK TABLE mysqltest.t1 WRITE;
 connect  con2,localhost,root,,;
-SET DEBUG_SYNC= 'now WAIT_FOR ready';
-SET DEBUG_SYNC= 'mdl_acquire_lock_wait SIGNAL ready';
+SET DEBUG_SYNC= 'now WAIT_FOR ready1';
+SET DEBUG_SYNC= 'mdl_acquire_lock_wait SIGNAL ready2';
 DROP DATABASE mysqltest;
 connect  con3,localhost,root,,;
-SET DEBUG_SYNC= 'now WAIT_FOR ready';
+SET DEBUG_SYNC= 'now WAIT_FOR ready2';
 connection default;
 FLUSH TABLES WITH READ LOCK;
 connection con3;

mysql-test/main/flush_read_lock.test

@@ -2106,15 +2106,16 @@ CREATE TABLE mysqltest.t1(a INT);
 HANDLER mysqltest.t1 OPEN as t1;
 
 connect (con1,localhost,root,,);
-SET DEBUG_SYNC= 'mdl_acquire_lock_wait SIGNAL ready';
+SET DEBUG_SYNC= 'mdl_acquire_lock_wait SIGNAL ready1';
 --send LOCK TABLE mysqltest.t1 WRITE
+
 connect (con2,localhost,root,,);
-SET DEBUG_SYNC= 'now WAIT_FOR ready';
-SET DEBUG_SYNC= 'mdl_acquire_lock_wait SIGNAL ready';
+SET DEBUG_SYNC= 'now WAIT_FOR ready1';
+SET DEBUG_SYNC= 'mdl_acquire_lock_wait SIGNAL ready2';
 --send DROP DATABASE mysqltest
 
 connect (con3,localhost,root,,);
-SET DEBUG_SYNC= 'now WAIT_FOR ready';
+SET DEBUG_SYNC= 'now WAIT_FOR ready2';
 
 connection default;
 send FLUSH TABLES WITH READ LOCK;