[test] Clobber unclean test262-es6 checkouts.

Review URL: https://codereview.chromium.org/1173753004

Cr-Commit-Position: refs/heads/master@{#28894}

test/test262-es6/testcfg.py

@@ -131,6 +131,16 @@ class Test262TestSuite(testsuite.TestSuite):
     archive_name = os.path.join(self.root, "tc39-test262-%s.tar.gz" % revision)
     directory_name = os.path.join(self.root, "data")
     directory_old_name = os.path.join(self.root, "data.old")
+
+    # Clobber if the test is in an outdated state, i.e. if there are any other
+    # archive files present.
+    archive_files = [f for f in os.listdir(self.root)
+                     if f.startswith("tc39-test262-")]
+    if len(archive_files) > 1 or archive_name not in archive_files:
+      print "Clobber outdated test archives ..."
+      for f in archive_files:
+        os.remove(os.path.join(self.root, f))
+
     if not os.path.exists(archive_name):
       print "Downloading test data from %s ..." % archive_url
       utils.URLRetrieve(archive_url, archive_name)