adds scheme, port and connection_options to fog connection

Hi there, thank you for this very helpful gem for CDN syncs! 

We switched from AWS to RiakCS and needed Proxy, Port and Scheme settings (as available as fog connection options). This can probably done with a broader approach with a hash as connection settings for fog, but was the most simple approach for know. Might be useful for others trying to use a Proxy or RiakCS.