test: rename test-regress-nodejsGH-3739

Rename the test appropriately alongside mentioning the subsystem
Also, make a few basic changes to make sure the test conforms
to the standard test structure

Refs: nodejs#19105
Refs: https://github.com/nodejs/node/blob/master/doc/guides/writing-tests.md#test-structure

Author: ryzokuken

test/parallel/test-regress-GH-3739.js renamed to test/parallel/test-fs-existssync-false.js

@@ -1,6 +1,10 @@
 'use strict';
-
 const common = require('../common');
+
+// This test ensures that fs.existsSync doesn't incorrectly return false
+// (especially on Windows)
+// https://github.com/nodejs/node-v0.x-archive/issues/3739
+
 const assert = require('assert');
 const fs = require('fs');
 const path = require('path');