tests/ioserver: disable nagle for control socket

We're sending one byte at a time here. For some reason on other
operating systems, there may be some optimizations going on, thus
disabling the latency; on others however I've observed the full
100-200ms cycle for each byte sent.

Change-Id: I87c266faacd70513264b3633d63c0c6c723753ac
Reviewed-on: http://review.couchbase.org/44401
Tested-by: Mark Nunberg <mnunberg@haskalah.org>
Reviewed-by: Sergey Avseyev <sergey.avseyev@gmail.com>