Fix issue with ember-cli reporting very low rebuild times

[mansona]

in the measureFileReload() function we have a call to waitForNetworkIdle() so that we can measure how long it takes for the browser to reload.

log("Waiting for hot reload to complete...");
await page.waitForNetworkIdle();

The problem is that in ember-cli the reload doesn't initiate until after the build finishes

Aside: an auto refresh is not a hot reload 🙈 hot reload is changing a module without refreshing the page