Bug 1411052 - Show local variables in wdspec tracebacks. r=maja_zf

Using the "--showlocals" pytest flag we can show the values of
variables in the local scope in the pytest tracebacks.  This seems
like a good thing to do to ease debugging.

Thanks-to: Dave Hunt <dave.hunt@gmail.com>

MozReview-Commit-ID: F62untoxEyi

--HG--
extra : rebase_source : db803258395e9bbacf10b06dc8ca367ae79ec67f

testing/web-platform/tests/tools/wptrunner/wptrunner/executors/pytestrunner/runner.py

@@ -56,6 +56,7 @@ def run(path, server_config, session_config, timeout=0):
                      "--verbose",  # show each individual subtest
                      "--capture", "no",  # enable stdout/stderr from tests
                      "--basetemp", cache,  # temporary directory
+                     "--showlocals",  # display contents of variables in local scope
                      "-p", "no:mozlog",  # use the WPT result recorder
                      "-p", "no:cacheprovider",  # disable state preservation across invocations
                      path],