The --repeat-until-failure can be very useful for finding flaky tests,
however sometimes it is hard to gauge how long it has left to run before
it can be considered successful.
This commit adds a small output showing the number of remaining runs
when the `--repeat-until-failure` flag is used.
It looks like:
```
Running ExUnit with seed: 382462, max_cases: 32, remaining_runs: 3
Excluding tags: [windows: true]
.......
Finished in 0.02 seconds (0.00s async, 0.02s sync)
Result: 7 passed
Running ExUnit with seed: 422319, max_cases: 32, remaining_runs: 2
Excluding tags: [windows: true]
.......
Finished in 0.00 seconds (0.00s async, 0.00s sync)
```
Gary Rennie
5b97e9c132