Handle network issues gracefully

[aarong]

When I perform an API request and I'm not connected to the internet I get:

Error: ETIMEOUT, Timeout while contacting DNS servers
at Timer.callback (dns.js:38:13)

Ideally timeouts would be passed to our callbacks as an error parameter, I think. And maybe we could set the timeout duration as an option as well? No sense waiting a minute (or whatever the default is) to tell the client that we can't reach SimpleDb.

Thanks again for an excellent module.