async-wrap: don't call init callback unnecessarily

Some calls to ReqWrap would get through the initial check and allow the
init callback to run, even though the callback had not been used on the
parent. Fix by explicitly checking if the parent has a queue.

Also change the name of the check, and internal field of AsyncHooks.
Other names were confusing.

PR-URL: https://github.com/iojs/io.js/pull/1614


Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>