`keybase prove web`: Failed to find a connection to ... (error 229): be more specific

```
$ keybase prove web ...
▶ ERROR Failed to find a connection to ... (error 229)
```

This error message could be _a lot_ more specific. (In my case, it's because I did not add an intermediate certificate to the web server config.)

Start by reproducing `keybase prove web ...` and trace where error 229 is generated. Review how connection and certificate failures are reported, then make the result more specific for cases such as a missing intermediate certificate; done when the command explains the likely cause instead of only showing the generic error.

Written by the indexing model from the issue text.