async_wrap: add uid argument to all asyncWrap hooks
By doing this, users can use a Map object for storing information instead of modifying the handle object.
@trevnorris mentioned this was an "API deficiency" https://github.com/nodejs/tracing-wg/pull/37/files#r48493114
Also, could we make uid
the first argument in the init
hook, such that it consistent for all hooks?