Bug 1351371 - Disable recommended automation prefs in CI; r=maja_zf

This tells Marionette to not set the recommended automation preferences in
testing/marionette/server.js when started.  We only want to use this set
of recommended prefs for public consumers of Marionette, and not when we
are testing Gecko itself as they may interfere with expectations of tests.

MozReview-Commit-ID: 4InVBRBnUTG

--HG--
extra : rebase_source : bfac0cff617651417cfa71ac0c80af73d583c827

testing/marionette/client/marionette_driver/geckoinstance.py

@@ -71,7 +71,12 @@ class GeckoInstance(object):
         "hangmonitor.timeout": 0,
 
         "javascript.options.showInConsole": True,
+
+        # Enable Marionette component
         "marionette.enabled": True,
+        # Disable recommended automation prefs in CI
+        "marionette.prefs.recommended": False,
+
         "media.volume_scale": "0.01",
 
         # Make sure the disk cache doesn't get auto disabled