MDEV-9713 Sporadic test failure: sys_vars.innodb_buffer_pool_load_now_basic

Previous fix using wait condition did not work because of MDEV-9867, so
we have to use conditional sleep instead. Sleep will only happen if the test
is executed after another one which also ran buffer pool dump without
server restart between two tests

mysql-test/suite/sys_vars/t/innodb_buffer_pool_load_now_basic.test

@@ -13,11 +13,19 @@ let $old_status= `SELECT variable_value FROM information_schema.global_status
 
 # A previous test could have run buffer pool dump already; 
 # in this case we want to make sure that the current time is different 
-# from the timestamp in the status variable
-
-let $wait_condition =
-  SELECT TRIM(SUBSTR('$old_status', -8)) != DATE_FORMAT(CURTIME(), '%k:%i:%s');
--- source include/wait_condition.inc
+# from the timestamp in the status variable.
+# We should have had a smart wait condition here, like the commented one below,
+# but we can't because of MDEV-9867, so there will be just sleep instead.
+# And it might be not enough to sleep one second, so we'll have to sleep two. 
+# let $wait_condition =
+#  SELECT TRIM(SUBSTR('$old_status', -8)) != DATE_FORMAT(CURTIME(), '%k:%i:%s');
+# -- source include/wait_condition.inc
+
+if (`SELECT variable_value LIKE '%dump completed at%' FROM information_schema.global_status
+     WHERE LOWER(variable_name) = 'innodb_buffer_pool_dump_status'`)
+{
+  -- sleep 2
+}
 
 # Do the dump
 SET GLOBAL innodb_buffer_pool_dump_now = ON;