tools: add --prof-process flag to node binary

This change cleans up outstanding comments on #3032. It improves error
handling when no isolate file is provided and adds the --prof-process
flag to the node binary which executes the tick processor on the
provided isolate file.

PR-URL: https://github.com/nodejs/node/pull/4021


Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Evan Lucas <evanlucas@me.com>