MDEV-18224 MTR's internal check of the test case 'innodb.recovery_shu…

…tdown' failed due to extra #sql-ib*.ibd files

The test innodb.recovery_shutdown would occasionally fail,
because recovered incomplete transactions would be conflicting
with DROP TABLE, causing the background drop table queue to be invoked.

Add a slow shutdown before dropping the tables, so that the
recovered transactions will be rolled back. Starting with MDEV-14705,
normal shutdown would abort the rollback of recovered transactions.

mysql-test/suite/innodb/t/recovery_shutdown.test

@@ -48,6 +48,12 @@ FLUSH TABLES;
 --let $shutdown_timeout=60
 --source include/restart_mysqld.inc
 
+# Perform a slow shutdown in order to roll back all recovered transactions
+# and to avoid locking conflicts with the DROP TABLE below.
+--disable_query_log
+SET GLOBAL innodb_fast_shutdown=0;
+--source include/restart_mysqld.inc
+
 --disable_query_log
 let $c = $trx;
 while ($c)