Incorrect error message when access key env vars missing

[austinbutler]

I had though I'd added my temporary AWS keys as env vars, but I hadn't, and when I went to use s3cmd I got the following errors:

ERROR: .s3cfg: None
ERROR: Configuration file not available.
ERROR: Consider using --configure parameter to create one.

I went looking to see if the configuration file was missing, but it wasn't. It's still there, with the access_token and such intentionally left blank in order to pull from the env vars.

From digging in a little bit, it seems this is because the error handling lumps a socket timeout and resulting 400 error from AWS into the same IOError you'd get if the file were missing. The timeout is from the call to self.role_config() in the Config class' init method, which for me results in a socket.timeout exception since I am running on my local machine versus an instance.

I may give a PR a go.