Auto merge of #15124 - cynicaldevil:pass-output, r=jdm

WPT tests now show debug ouput for passing tests as well

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- [X] `./mach build -d` does not report any errors
- [X] `./mach test-tidy` does not report any errors
- [X] These changes fix (partially) #12808
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@jdm I thought it would be better to make a PR for my local changes anyway, since you wanted it :)
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tests/wpt/run.py

@@ -31,7 +31,11 @@ def run_tests(paths=None, **kwargs):
 
     mozlog.commandline.log_formatters["servo"] = \
         (grouping_formatter.GroupingFormatter, "A grouping output formatter")
-    wptrunner.setup_logging(kwargs, {"servo": sys.stdout})
+
+    if len(kwargs["test_list"]) == 1:
+        wptrunner.setup_logging(kwargs, {"mach": sys.stdout})
+    else:
+        wptrunner.setup_logging(kwargs, {"servo": sys.stdout})
 
     success = wptrunner.run_tests(**kwargs)
     return 0 if success else 1