Fix for situation where swarm leave causes wait forever for agent to stop

In this case the message to stop the agent is never actually sent
because the swarm node is nil

Signed-off-by: Kyle Wuolle <kyle.wuolle@gmail.com>
Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

daemon/cluster/noderunner.go

@@ -298,6 +298,11 @@ func (n *nodeRunner) Stop() error {
 		n.cancelReconnect = nil
 	}
 	if n.swarmNode == nil {
+		// even though the swarm node is nil we still may need
+		// to send a node leave event to perform any cleanup required.
+		if n.cluster != nil {
+			n.cluster.SendClusterEvent(lncluster.EventNodeLeave)
+		}
 		n.mu.Unlock()
 		return nil
 	}