Add back support for --endpoint-url option to s3

[mguillaume]

The --endpoint-url option was re-enabled with commit d6c46df but s3 uses different code to get the endpoint.
This adds back endpoint-url support for the s3 service.

[mguillaume]

Looks like I have to adapt the unit tests too, I'll update ASAP.

[jamesls]

Could you also add a unit tests for your change? That way we can ensure we don't regress on this again in the future.

Thanks.

[mguillaume]

I think this one does it.
Note that for S3, without specifying a region, endpoint-url will not work as botocore has to do a lot of "magic" associated with region endpoints and DNS compatible endpoints. I have a (pretty simple) pull request in botocore to allow us to use --region=mock for this: boto/botocore#171

[jamesls]

Thanks for adding the test, looks good. Looks like there were other changes to s3 recently so there are a few merge conflicts I'll have to work through. Unless of course you wouldn't mind rebasing against develop :)

[mguillaume]

This is "rebased" (manually + push -f), but one test does not pass anymore.
I'm not 100% sure but I think the Mock service for s3 doesn't provide everything that is required by the new ListCommand.

[jamesls]

Sorry for the delay, this has been merged, thanks!