WSGI integration does nonstandard split between http.host and http.url

[Oberon00]

See https://github.com/open-telemetry/opentelemetry-specification/blob/master/specification/data-semantic-conventions.md#http-server and https://github.com/open-telemetry/opentelemetry-python/blob/master/ext/opentelemetry-ext-wsgi/src/opentelemetry/ext/wsgi/__init__.py#L49-L56.

Even though the code seems right (apart from removing the query which should be included according to spec and adding a nonstandard http.host attribute), using a dumb flask example app (not the one from this repo, but that should work too), this resulted for me

k	t	v
http.url	str	/hello-opentelemetry
http.host	str	localhost:5000

Maybe there is a bogus value in one of the environment variables.

I will hopefully have time to investigate tomorrow, but if someone is quicker, fell free to take this issue.

[Oberon00]

CC @a-feld

[Oberon00]

Found the "culprit": https://github.com/pallets/werkzeug/blob/master/src/werkzeug/serving.py#L202-L205

[Oberon00]

Due to the squash-merge, the issue did not get closed automatically by #148, closing it now (note that the related #173 is also merged).