inspector: Do cleanups before notifying callback

Inspector socket implementation was notifying handshake callback before
performing the cleanups, which meant that callback could not reclaim
resources allocated by the client. New implementation will free all
resource not allocated by the client before calling the callback,
allowing the client to complete the cleanup.

Fixes: https://github.com/nodejs/node/pull/7418
PR-URL: https://github.com/nodejs/node/pull/7450


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