ZTS: Fix zfs_mount.kshlib cleanup

Update cleanup_filesystem to use destroy_dataset when performing
cleanup.  This ensures the destroy is retried if the pool is busy
preventing occasional failures.

Reviewed-by: George Melikov <mail@gmelikov.ru>
Reviewed-by: Giuseppe Di Natale <guss80@gmail.com>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes openzfs#10358

tests/zfs-tests/tests/functional/cli_root/zfs_mount/zfs_mount.kshlib

@@ -110,7 +110,7 @@ function cleanup_filesystem #pool #fs
 
 	if datasetexists "$pool/$fs" ; then
 		mtpt=$(get_prop mountpoint "$pool/$fs")
-		log_must zfs destroy -r $pool/$fs
+		destroy_dataset "$pool/$fs" "-r"
 
 		[[ -d $mtpt ]] && \
 			log_must rm -rf $mtpt