[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/498807Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Commit-Queue: Michael Achenbach <machenbach@chromium.org>
Cr-Commit-Position: refs/heads/master@{#45178}

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.