adding tcp keepalive support for the broker's tcp connection

[epsniff]

We've been using the sarama client on Google Compute Engine (GCE) and it works well, expect that once in a while we get read tcp 10.240.20.4:9093: i/o timeout. This occurs often with Go sockets on GCE, because GCE kills idle connections after 10 mins and by default Go's net package turns off tcp keepalives.

I've created a small patch to support keepalives: lytics@76aa551. Let me know if you have any feedback? We're currently running these changes through our staging environment to see this fixes the issue.

Ref: https://cloud.google.com/compute/docs/troubleshooting#communicatewithinternet

thanks for all your hard work!!!

[eapache]

Sounds like a good idea, although based on http://felixge.de/2014/08/26/tcp-keepalive-with-golang.html it looks like keepalives in golang are rather inconsistent across platforms. For style, you may want to take a look at #154 which also adds parameters to the dialer; it may be cleaner to follow that pattern than to wrap it up in an extra function.

[epsniff]

Thank you for looking. Ill look at both and clean up the code accordingly.

[epsniff]

Closing the ticket after my PR got merged.