Use cookie to dismiss help dialog and fix failing browser tests

I have seen this failing:
https://integration.wikimedia.org/ci/job/mwext-mw-selenium-jessie/9255/console

The idea is to pre-set this cookie so the help dialog never shows up
in the first place. The tests do not need to look for the element, click
it, wait for the dialog to close. This should even speed up the browser
tests, I believe.

Also this adjustes waiting conditions in several places to address
timing issues with failing browser tests.

Since these tests should be replaced by Node.js on the long run I
added "sleep" in the cases although it's not recommended.

Change-Id: Ida381faa390aa62ebaadd3713864676be80abd51