make visual regression sleep duration configurable

[timstoddard]

Desired Behavior

Make an option called visualRegressionSleepDuration that sets the amount of time to wait after Angular loads the component and all the network requests are idle. Defaults to 100ms.

[ddehghan]

Yes. this is very much needed. we sometime get blank screens and I think that is a timing issue. Since we run this regression test offline we can afford giving it much more time to finish to account for the CPU load on the build server.