Keep a running count of failed tests next to the progress bar

[smarter]

Currently, when running tests, we display a progress bar that looks like this:

[========>                              ] completed (393/1573, 85s)

But nothing here tells you how many tests have failed so far, which can be useful information to decide whether to keep running the tests or abort them early, we could display it like this:

[========>                              ] completed (393/1573, 85s, 10 failed)