As of recently, osquery will report when a distributed query fails. We now
expose errors over the results websocket. When a query errored on the host, the
`error` key in the result will be non-null. Note that osquery currently doesn't
provide any details so the error string will always be "failed". I anticipate
that we will fix this and the string is included for future-proofing.
Successful result:
```
{
"type": "result",
"data": {
"distributed_query_execution_id": 15,
"host": {
... omitted ...
},
"rows": [
{
"hour": "1"
}
],
"error": null
}
}
```
Failed result:
```
{
"type": "result",
"data": {
"distributed_query_execution_id": 14,
"host": {
... omitted ...
},
"rows": [
],
"error": "failed"
}
}
```
