IOCP: Migrate to read2

Change-Id: I1d6d9f2a037d0d199452e4422e49aab60d44aaf9
Reviewed-on: http://review.couchbase.org/36089
Reviewed-by: Brett Lawson <brett19@gmail.com>
Tested-by: Mark Nunberg <mnunberg@haskalah.org>