Change zfs arguments. This also works with older zfs versions, tested with
zfs 0.7.9-3 on Ubuntu 18.10.

Closes #2916.
Signed-off-by: Paul Gauret <pgauret@yahoo.com>
[christian.brauner@ubuntu.com: adapt commit message and add Signed-off-by for Paul]
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>