[Test] Update all SixSpeed tests to run in separate processes.

test/js-perf-test/SixSpeed/run.js

 // Copyright 2017 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-load('../../base.js');
+load('../base.js');
 load(arguments[0] + '.js');
 
 var success = true;
 
 function PrintResult(name, result) {
   print(name + '(Score): ' + result);
 }
 
 function PrintError(name, error) {
   PrintResult(name, error);
   success = false;
 }
 
 BenchmarkSuite.config.doWarmup = true;
 BenchmarkSuite.config.doDeterministic = undefined;
 
 BenchmarkSuite.RunSuites({NotifyResult: PrintResult, NotifyError: PrintError});