Don't report error on cleanly closed SSL connections

When reading from an SSL connection, check for normal (clean)
connection close; don't report it as an error.

Change-Id: Ia4912489cafc893fa237b165be011fe13c28f711
Reviewed-on: http://review.couchbase.org/43605
Tested-by: buildbot <build@couchbase.com>
Reviewed-by: Trond Norbye <trond.norbye@gmail.com>