add a line to re-run the failed test after each failure in the compact reporter

[jakemac53]

Closes #1734

Example output:

[jakemac53]

For now I did this only in the compact reporter, because it only ever runs on the VM (and I have access to Platform.executable). The expanded reporter runs on the web etc, and it isn't clear how to replicate the same functionality.

There is also a bit of a question I think in terms of internal, but I believe we always use a different reporter so they won't ever see it.

[jakemac53]

I also wonder if I shouldn't move the command down to the next line, which would make it easier to copy/paste?

[Hixie]

Is there a way to disable this message? It shows up for flutter test test failures but the command it gives doesn't work to actually run the test again.