Add Engine version to docker node ls

This adds the Engine version to `docker node ls`, and `.EngineVersion` as a
template option.

With this patch applied:

    docker node ls
    ID                            HOSTNAME                STATUS              AVAILABILITY        MANAGER STATUS      ENGINE VERSION
    wp9231itoqsh4rqceojqo01vp *   linuxkit-025000000001   Ready               Active              Leader              18.01.0-ce

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

internal/test/builders/node.go

@@ -125,3 +125,10 @@ func ManagerStatus(managerStatusBuilders ...func(*swarm.ManagerStatus)) *swarm.M
 
 	return managerStatus
 }
+
+// EngineVersion sets the node's engine version
+func EngineVersion(version string) func(*swarm.Node) {
+	return func(node *swarm.Node) {
+		node.Description.Engine.EngineVersion = version
+	}
+}