Include host in client error messages

[tpoliaw]

Currently, when the client fails to connect it gives a bit of a vague error message

Error querying service: error sending request

which isn't very helpful. Something like

Error querying service: Could not connect to https://numtracker.example.com

would be more useful, especially when you're expecting it to connect to https://numtracker.diamond.ac.uk

[tpoliaw]

It's not clear where this error is coming from as all connection errors appear to be being displayed as expected - possibly from the openidconnect library we're using. For now #230 should increase logging around what configuration is being used and where it's sourced which should help debug further issues.

[tpoliaw]

The error is easiest to reproduce by running against localhost when there is no server running