Add support for Google Cloud Storage (boto.connect_gs)

[rdodev]

First, really nice little mocking library you got going.

Second, it would be super nice if you could add support for mocking boto.connect_gs().

Thanks.

[spulec]

I don't have a lot of time right now, but it looks pretty similar to S3. Happy to take a pull request if someone wants to work on it.

[dmlayton]

I would love to get this working, but figuring out how mock_s3 works. connect_s3 does not appear to be the entry point.

[terricain]

Do we still need this?

[JackDanger]

Due to Boto3's lack of plans to support Google Cloud Storage I'm going to close this for now: boto/boto3#579