test: speed up test-child-process-spawnsync.js

There's a bunch of stuff in test-child-process-spawnsync.js that seems
designed to test that it is in fact blocking/synchronous. However, that
code really just tests the OS sleep command. Change `sleep 1` to `sleep
0` and shave about one second off the test run.`

We check the return status to confirm the command is successful. The
tests in this file in general would not work if spawnSync() were
asynchronous. That includes this one, as a return status would not be
available if the command where asynchronous.

PR-URL: https://github.com/nodejs/node/pull/2542


Reviewed-By: Colin Ihrig <cjihrig@gmail.com>