longhorn: Run on dedicated nodes

I've created new worker nodes that are dedicated to running Longhorn
replicas.  These nodes are tainted with the
`node-role.kubernetes.io/longhorn` taint, so no regular pods will be
scheduled there by default.  Longhorn pods thus needs to be configured
to tolerate that taint, and to be scheduled on nodes with the
similarly-named label.

storage/longhorn-settings.yaml

@@ -3,4 +3,4 @@ kind: Setting
 metadata:
   name: taint-toleration
   namespace: longhorn-system
-value: du5t1n.me/machine=raspberrypi:NoExecute
+value: du5t1n.me/machine=raspberrypi:NoExecute;node-role.kubernetes.io/longhorn:NoSchedule