MDEV-21421 : Galera test sporadic failure on...

MDEV-21421 : Galera test sporadic failure on galera.galera_as_slave_gtid_myisam: Result length mismatch

Add wait_condition so that drop table has time to replicate to
Galera cluster.

mysql-test/suite/galera/r/galera_as_slave_gtid_myisam.result

@@ -23,6 +23,9 @@ gtid_binlog_state_equal
 #cleanup
 connection node_1;
 DROP TABLE t1;
+connection node_2;
+connection node_3;
+connection node_1;
 reset master;
 connection node_2;
 STOP SLAVE;

mysql-test/suite/galera/t/galera_as_slave_gtid_myisam.test

@@ -55,6 +55,16 @@ SELECT COUNT(*) = 0 FROM t1;
 --echo #cleanup
 --connection node_1
 DROP TABLE t1;
+
+--connection node_2
+--let $wait_condition = SELECT COUNT(*) = 0 FROM INFORMATION_SCHEMA.TABLES WHERE TABLE_NAME = 't1';
+--source include/wait_condition.inc
+
+--connection node_3
+--let $wait_condition = SELECT COUNT(*) = 0 FROM INFORMATION_SCHEMA.TABLES WHERE TABLE_NAME = 't1';
+--source include/wait_condition.inc
+
+--connection node_1
 reset master;
 
 --connection node_2