This should be the last one right now. We already added the
dm-service-time alternate load balancer. But some setups may
want the slightly different approach dm-queue-length offers.

BugLink: https://bugs.launchpad.net/bugs/1673350Signed-off-by: Stefan Bader <stefan.bader@canonical.com>
Acked-by: Colin King <colin.king@canonical.com>
Acked-by: Tim Gardner <tim.gardner@canonical.com>
Acked-by: Seth Forshee <seth.forshee@canonical.com>
Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@canonical.com>