Don't raise an error if server doesn't implement the migrations endpoint

[giovannibenussi]

There are some cases where the /v1/jobs endpoint doesn't exist so this API call returns a 404 and makes the client to fail. This PR handles this case without raising an error.

[giovannibenussi]

I added some extra debugging information in case this function throws an error. It looks like this:

This is useful for us because when a user reports an error we can know exactly which URL and status code they got from the server. This way we can know if the issue is localhost, http(s) or ws(s).