test: disable eio-race tests

Disabled the following unit tests:

* test-eio-race.js
* test-eio-race2.js
* test-eio-race4.js

These tests are known to fail on busy boxes due to being timing sensitive,
and are deemed not meaningful tests.

See https://github.com/joyent/node/issues/4272

Fixes #4272.

test/simple/test-eio-race2.js → test/disabled/test-eio-race2.js

@@ -41,5 +41,3 @@ setTimeout(function() {
     });
   }
 }, 100);
-
-