Update "wait" utility functions for tests with Selenium Wait API

[valentijnnieman]

There are a couple of functions we're using in our tests, for example the wait_for style functions in the utils.py file, that we could update to use https://selenium-python.readthedocs.io/waits.html instead of our own functions.

[alexcjohnson]

@byronz I'm going to close this one, I think you have a good handle on wait_for and have already made some changes along the lines suggested here.