Add detailed error descriptions in the matcher

[aby2s]

Error descriptions in the matcher look like:

'message': 'Could not find a valid OpenAPI schema for path=/pets, method=get'

It also matches a hostname and, probably, query params. We should show them all. And we should show the source of an error if we can. I mean, if there is no spec matching a hostname, we should return something like "No matching host found for ...".