Implement OTA Agent that pulls from the cloud

### Description

Currently, to update a POD with either an access point or via direct connection (over some protocol), it is required to have the update file locally. Current invocation for updates looks something like this:

```iotile hw --port=virtual:reference_1_0 connect 1 app --name device_updater load_script ```

This new implementation will instead have a slightly different functional path that checks for an update from the cloud, then applies if it one is ready for a device. Possible command would look something like this:

```iotile hw --port= connect 1 app --name cloud_ota --device update```

The program flow will implement
1. (optional / possible) Pull current device version
2. Check if the cloud has a newer version *or* is serving an update for the devId
3. Download update and send to the device
4. Wait for update to be complete
5. Tell cloud that update has been completed

Reference card https://github.com/orgs/iotile/projects/17#card-13237757