Fix authentication URL port handling

[maci3jka]

When the cluster URL includes a non-default port (non 443) and the verification URL does not specify one, the browser was opened to the wrong host — missing the port entirely and causing the authentication flow to fail.
Example that I faced when port forwarding k8s service

$engflow_auth login --insecure localhost:8443
Warning: server TLS validation is disabled
Attempting to automaticaly open the authentication URL in your web browser.
If the browser does not open or you wish to use a different device to authorize this request, open the following URL:

        https://localhost/login?userCode=XXXX-YYYY-ZZZZ&redirect=QWERTY123==

[laszlocsomor]

Please rebase; CI should pass at f1ab63d

[maci3jka]

Please rebase; CI should pass at f1ab63d

@laszlocsomor done

[laszlocsomor]

And please describe in the PR message what was the bug. Looks like when the cluster listens on a nonstandard port, the verification URL should contain it too, but please confirm.

When would this be a problem, I mean in what case do you access a cluster on a nonstandard port?

[maci3jka]

I've faced

$engflow_auth login --insecure localhost:8443
Warning: server TLS validation is disabled
Attempting to automaticaly open the authentication URL in your web browser.
If the browser does not open or you wish to use a different device to authorize this request, open the following URL:

        https://localhost/login?userCode=XXXX-YYYY-ZZZZ&redirect=QWERTY123==

this pr fixes that. I've updated the description