Fixed failures in innodb tests caused by not flushed restart

- Fixed innodb.recovery_shutdown.test
- Fixed innodb.instant_alter_rollback

mysql-test/suite/innodb/r/instant_alter_rollback.result

+FLUSH TABLES;
 #
 # MDEV-11369: Instant ADD COLUMN for InnoDB
 #

mysql-test/suite/innodb/r/recovery_shutdown.result

+FLUSH TABLES;
 #
 # MDEV-13797 InnoDB may hang if shutdown is initiated soon after startup
 # while rolling back recovered incomplete transactions

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

@@ -2,6 +2,9 @@
 # The embedded server tests do not support restarting.
 --source include/not_embedded.inc
 
+# Flush any open myisam tables from previous tests
+FLUSH TABLES;
+
 --echo #
 --echo # MDEV-11369: Instant ADD COLUMN for InnoDB
 --echo #

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

 --source include/have_innodb.inc
 --source include/not_embedded.inc
 
+# Flush any open myisam tables from previous tests
+FLUSH TABLES;
+
 --echo #
 --echo # MDEV-13797 InnoDB may hang if shutdown is initiated soon after startup
 --echo # while rolling back recovered incomplete transactions