Reland "[test] Don't flatten testcfg globals"

This reverts commit 4fdf7cdf.

Reason for revert: Fixed

Original change's description:
> Revert "[test] Don't flatten testcfg globals"
> 
> This reverts commit 4fa473cb.
> 
> Reason for revert: Problems when v8 isn't located in a folder called "v8".
> 
> Original change's description:
> > [test] Don't flatten testcfg globals
> > 
> > This loads each test's testcfg.py as a unique module rather than flattening all into testcfg. Other than accessing LoadTestSuite there should be no references into testcfg files.
> > 
> > Bug: v8:6375
> > Change-Id: If863c1b35096b2589111e8091bb7d68f135da674
> > Reviewed-on: https://chromium-review.googlesource.com/498807
> > Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
> > Commit-Queue: Michael Achenbach <machenbach@chromium.org>
> > Cr-Commit-Position: refs/heads/master@{#45178}
> 
> TBR=jkummerow@chromium.org,machenbach@chromium.org
> NOPRESUBMIT=true
> NOTREECHECKS=true
> NOTRY=true
> Bug: v8:6375
> 
> Change-Id: I3600b54279c0d98a39475432c5b2163f510153f0
> Reviewed-on: https://chromium-review.googlesource.com/500130
> Reviewed-by: Michael Achenbach <machenbach@chromium.org>
> Commit-Queue: Michael Achenbach <machenbach@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#45180}

TBR=jkummerow@chromium.org,machenbach@chromium.org,v8-reviews@googlegroups.com
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
Bug: v8:6375

Change-Id: I8198b74ff8e1c3aa179769bef24f204dc705da67
Reviewed-on: https://chromium-review.googlesource.com/500131Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Commit-Queue: Michael Achenbach <machenbach@chromium.org>
Cr-Commit-Position: refs/heads/master@{#45181}

tools/testrunner/local/testsuite.py

@@ -71,7 +71,7 @@ class TestSuite(object):
     f = None
     try:
       (f, pathname, description) = imp.find_module("testcfg", [root])
-      module = imp.load_module("testcfg", f, pathname, description)
+      module = imp.load_module(root + "_testcfg", f, pathname, description)
       return module.GetSuite(name, root)
     except ImportError:
       # Use default if no testcfg is present.