ioutils: don't enumerate errors for EFAIL

We're returning EFAIL on anything not explicitly caught above.

Change-Id: I8bb61ecb9dadc25d79d85c34f7836a556bfabd07
Reviewed-on: http://review.couchbase.org/36250
Reviewed-by: Brett Lawson <brett19@gmail.com>
Tested-by: Mark Nunberg <mnunberg@haskalah.org>