Fix auto_stub.py for skipped tests.

This is blocking a luci roll in infra.

R=nodir@chromium.org

Change-Id: I996a74ba519cf05f72d430ca4a2e63e76436b509
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/1598469
Reviewed-by: Nodir Turakulov <nodir@chromium.org>
Commit-Queue: Marc-Antoine Ruel <maruel@chromium.org>

testing_support/auto_stub.py

@@ -70,4 +70,7 @@ class TestCase(unittest.TestCase, AutoStubMixIn):
 
   def has_failed(self):
     """Returns True if the test has failed."""
+    if not self._resultForDoCleanups:
+      # Maybe skipped.
+      return False
     return not self._resultForDoCleanups.wasSuccessful()