tools: copy run-valgrind.py to tools/

It was a symbolic link to deps/v8/tools/run-valgrind.py before.  We are
going to make changes to it and we don't want to carry the patch forward
so make a copy.

PR-URL: https://github.com/nodejs/node/pull/9520


Reviewed By: Sakthipriyan Vairamani <thechargingvolcano@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Michael Dawson <michael_dawson@ca.ibm.com>