Do not wait indefinitely when connecting to a server/ip that does not respond

When entering a server/ip that does not respond, after clicking "connect" the user waits too much time. When clicking on "connect", we try a lot of URLs to guess if the server supports OAuth2 or nuxeo-platform-login-token, each try having a big timeout.

We should try to test if the server responds with a short timeout before testing which authentication method the app will use.
each try should also have a quite short timeout to prevent any blocking request.