Don't print out warnings if socket is closed

Change-Id: I847f11ff1e0d4341f3757106bee488e7e46e496e
Reviewed-on: http://review.couchbase.org/32678
Reviewed-by: Trond Norbye <trond.norbye@gmail.com>
Tested-by: Trond Norbye <trond.norbye@gmail.com>