deflake TestNavigateWhileLoading
deflake TestNavigateWhileLoading

This commit does not fix the implementation of responseAction()
since there is not way to tell whether the events are from the
first navigate.

It just change the test to make sure the Page.lifecycleEvent with
the name "init" is emitted before starting the second navigate.

Fixes #1080

chromedp/chromedp,chromedp/chromedp,chromedp/chromedp