iotile hw scan --reverse is broken

The `iotile hw scan` command takes a `--reverse` flag that should reverse the sort order of results. It appears to be ignored. It is most useful when combined with `--limit` to get the last N uuids seen in a scan:

```
(HardwareManager) scan -r -l 1
{
"advertising_version": 1,
"expiration_time": "2019-03-06 08:24:37.851276",
"low_voltage": false,
"pending_data": false,
"signal_strength": -81,
"slug": "d--0000-0000-0000-00f7",
"user_connected": false,
"uuid": 247
}
(HardwareManager) scan -l 1
{
"advertising_version": 1,
"expiration_time": "2019-03-06 08:24:37.851276",
"low_voltage": false,
"pending_data": false,
"signal_strength": -81,
"slug": "d--0000-0000-0000-00f7",
"user_connected": false,
"uuid": 247
}
```

In both cases the sort order was unchanged.