build: simplify execution of built binary
build: simplify execution of built binary

Since we aleady have a variable with path to the newly built
binary, use that instead of prefixing path. This also allows us
to pass a different path through the environment (NODE=)

PR-URL: https://github.com/nodejs/io.js/pull/1955
Reviewed-By: Ben Noordhuis <59bd0a3ff43b32849b319e645d4798d8a5d1e889@bnoordhuis.nl>
Reviewed-By: Rod Vagg <f9f03903429036ef609ed7ca822fddfa76155c29@vagg.org>

dreamllq/node,dreamllq/node,dreamllq/node,dreamllq/node,dreamllq/node,dreamllq/node,dreamllq/node,dreamllq/node,dreamllq/node