Stop nodes added to the blocklist

[andrerenard]

Currently if a running node is added to the blocklist, it will keep running. This can cause array synchronization issues, since coco stops updating that node. Ideally we shouldn't have to rely on someone remembering to also stop the kotekan service on that node, and just issue a /kill call from coco to any node added to the block list. If the node already happens to be stopped the call will have no effect.