innodb_preshutdown(): Only wait for active transactions to be terminated
if InnoDB was started and innodb_force_recovery=3 or larger does not
prevent a rollback.

This fixes the following:

./mtr --parallel=auto --mysqld=--innodb-fast-shutdown=0 \
innodb.log_file_size innodb.innodb_force_recovery \
innodb.read_only_recovery innodb.read_only_recover_committed \
mariabackup.apply-log-only-incr