end2end tests: Don't fail with "STUB:" warnings

We have some things like pos_px stubbed which will fail any test because
of the stub warning - but some tests don't actually need that, it just
happens when e.g. loading something.

So let's not fail tests based on stub warnings, and see how much works
that way.

tests/end2end/fixtures/quteprocess.py

@@ -305,7 +305,10 @@ class QuteProc(testprocess.Process):
         is_ddg_load = testutils.pattern_match(
             pattern="load status for <* tab_id=* url='*duckduckgo*'>: *",
             value=msg.message)
-        return msg.loglevel > logging.INFO or is_js_error or is_ddg_load
+
+        is_log_error = (msg.loglevel > logging.INFO and
+                        not msg.message.startswith('STUB:'))
+        return is_log_error or is_js_error or is_ddg_load
 
     def _maybe_skip(self):
         """Skip the test if [SKIP] lines were logged."""