TT#56376 selenium: reduce geckodriver console logs

testrunner
- reduce geckodriver logs to fatal errors
- this will not supress all logs, since the rest are generated by
firefox/marionette and this setting cannot be changed easily

Change-Id: I96b2f8731aa23af85dc8a32de56a19e1a9f7c2f7
(cherry picked from commit 0ab14718cc)

t/selenium/testrunner

@@ -53,10 +53,10 @@ firefox --version
 
 # ensure we don't leave any process behind causing problems with re-execution
 pkill -f 'geckodriver' || true
-DISPLAY=:99 ~/geckodriver -p 4444 &
-DISPLAY=:99 ~/geckodriver -p 5555 &
-DISPLAY=:99 ~/geckodriver -p 6666 &
-DISPLAY=:99 ~/geckodriver -p 7777 &
+DISPLAY=:99 ~/geckodriver -p 4444 --log fatal &
+DISPLAY=:99 ~/geckodriver -p 5555 --log fatal &
+DISPLAY=:99 ~/geckodriver -p 6666 --log fatal &
+DISPLAY=:99 ~/geckodriver -p 7777 --log fatal &
 
 echo "################################################################################"
 echo "Finished main setup, now running tests ..."