machine.action does not always throw errors for failed machines

[Peter Makowski]

Currently the websocket API responds to machine.action performed with a filter only with a number of nodes that the action was performed on successfully, even if an action could not be performed on some of the nodes requested (e.g. when trying an action that's not supported, like test on a machine that's already being tested).

request: request_id: 25, method: "machine.action", params: {action: "test", filter: {id: ["tw8pfr", "b3ye4t"]}}

response: { request_id: 25, result: 1 }

We need either an error message or a list of failed machines to be added to the response (system_ids/names).