Bug 1401489 - Generate wptreport json files for web-platform tests in CI, r=maja_zf

This uploads a JSON summary of the results, without extra logging or
expectation data or anything. It is mostly useful for comparing the
results from two runs e.g. in a dashboard.

MozReview-Commit-ID: Ac45NVBxhy8

Author: jgraham

testing/mozharness/scripts/web_platform_tests.py

@@ -186,6 +186,8 @@ def _query_cmd(self):
         cmd += ["--log-raw=-",
                 "--log-raw=%s" % os.path.join(dirs["abs_blob_upload_dir"],
                                               "wpt_raw.log"),
+                "--log-wptreport=%s" % os.path.join(dirs["abs_blob_upload_dir"],
+                                                    "wptreport.json"),
                 "--log-errorsummary=%s" % os.path.join(dirs["abs_blob_upload_dir"],
                                                        "wpt_errorsummary.log"),
                 "--binary=%s" % self.binary_path,