Event testing integration with power control testing.

* register_event fixture implanted in the tests
* modified event testing to collect results after each test run
* polling the listener now uses the wait_for to speed things up in case of success
* changed the format of the output HTML, events are grouped by tests
* added _wait_for_results_refresh() on places that needed it
* Infra. provider / Add / Validate button fix
* Info text when starting the tests with event testing on to open the desired port in firewall together with the correct command to do it

In previous PR, wait_for was implanted into vm power control in pages/ so this speeds things up too.