Improve behat resilience with pendingJS

Improve use of our JS in behat with pending promise.

This issue covers a number of areas where I've encountered random behat failure because Behat was trying to perform the next action before the page had finished doing it's job.

Note: You may not be able to reproduce any of the original issues. Mostly they start to show up when we upgrade our webdriver. This is likely because newer versions of Firefox are more efficient than the versions we're testing against right now. It may also be due to performance improvements in the W3C webdriver vs. the JsonWire specification.