Revise authentication parameters for connector methods

What is the expected behavior?

Currently, most of the methods of IBMQConnector that interact with and endpoint accept the credentials information (hub, group, user_id, etc) as parameters, and perform a similar set of operations at the beginning of the function:

        if access_token:
            self.req.credential.set_token(access_token)
        if user_id:
            self.req.credential.set_user_id(user_id)
        if not self.check_credentials():
            raise CredentialsError('credentials invalid')

However, the credentials information is already present in self.config, which makes the parameters and some checks redundant (and actually, the parameters are unused by the rest of the codebase). It seems a good candidate for simplification, by just removing the parameters and fetching the needed information from self.config directly.

[jwoehr]

Thank you. I’ll do this.

[diego-plan9]

Fixed via #56