errors: make dns errors consistent

Right now the hostname could in some cases be missed, depending on
the libuv error number. This makes sure there the hostname is always
added, if available.

PR-URL: https://github.com/nodejs/node/pull/19754


Reviewed-By: Joyee Cheung <joyeec9h3@gmail.com>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>