check update status to report errors on `build` and `update`

[lukelafountaine]

Currently, the build and update commands assume success.

Since these commands are asynchronous, we need to make successive calls to check on the status of the operation. The SMAPI docs mention that the response for these requests contain a Location header which is a relative URL that can be used to track the status. This PR makes use of that Location URL to report any actual errors that have happened.

[driskell]

Thanks for this - it really helped work out why things were failing!