test: fix test-debug-port-numbers on OS X

According to kill(2), kill returns `EPERM` error if when signalling a
process group any of the members could not be signalled.

PR-URL: #7046
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>

Author: santigimeno

test/parallel/test-debug-port-numbers.js

@@ -44,7 +44,9 @@ function kill(child) {
   try {
     process.kill(-child.pid);  // Kill process group.
   } catch (e) {
-    assert.strictEqual(e.code, 'ESRCH');  // Already gone.
+    // Generally ESRCH is returned when the process group is already gone. On
+    // some platforms such as OS X it may be EPERM though.
+    assert.ok((e.code === 'EPERM') || (e.code === 'ESRCH'));
   }
 }