Add check for empty socket.error args

[gustafsson]

When doing a

gsutil cp myfile gs://mybucket/name

With a https_proxy that was limiting the number of concurrent sockets. I got a

socket.timeout: timed out

During handling of the above exception, another exception occurred:
...
socks.GeneralProxyError: Socket error: timed out

During handling of the above exception, another exception occurred:
...
~/Applications/google-cloud-sdk/platform/gsutil/gslib/gcs_json_media.py", line 587, in _conn_request
    err = getattr(e, 'args')[0]

It seems socket.error can have empty args. This PR adds a check.

gsutil_IndexError_tuple_index_out_of_range.txt

[dilipped]

Sorry for the late response here and thanks for the PR. Can you please add tests for the change? The test can go in the file tests/test_gcs_json_media.py.

[dilipped]

You can replace the entire line with if getattr(e, 'args', None)