NCBC-357: Set TCP Keep Alives on Connections

Change-Id: I2de9d44b7622e5adcc0bb8c163279b8690aea4f8
Reviewed-on: http://review.couchbase.org/31807
Reviewed-by: Brett Lawson <brett19@gmail.com>
Tested-by: Jeffry Morris <jeffrymorris@gmail.com>