Don't create custom iops in db

This allows us to test against other event loops using the default
environment variables for such things.

Change-Id: I065b51a0d7c7037c26ca4cba94630408939bdf1d
Reviewed-on: http://review.couchbase.org/26913
Reviewed-by: Sergey Avseyev <sergey.avseyev@gmail.com>
Tested-by: Mordechai Nunberg <mnunberg@haskalah.org>