Merge: nitunit: improve progress display

The results are printed progressively instead of at the end of each test-suite.
The progress bar in therefore displayed below the results.

See it in action: https://asciinema.org/a/17u9jwts0nz5dfpxp8p9aab0f

Pull-Request: #2156
Reviewed-by: Alexandre Terrasa <alexandre@moz-code.org>