Bug 1617626 - [remote] Enable trace level logs for browser-chrome tests in CI. r=ahal

Differential Revision: https://phabricator.services.mozilla.com/D68644

--HG--
extra : moz-landing-system : lando

taskcluster/ci/test/mochitest.yml

@@ -455,3 +455,5 @@ mochitest-remote:
     max-run-time: 5400
     mozharness:
         mochitest-flavor: browser
+        extra-options:
+            - --setpref=remote.log.level=Trace