Fix the reproduction script for testFromTasty tests

[nicolasstucki]

For example a failure in a testFromTasty for tests/run/eff-dependent.scala will output the following report:

================================================================================
Test Report
================================================================================

1 suites passed, 1 failed, 2 total
    tests/run/eff-dependent.scala failed


Test 'tests/run/eff-dependent.scala' compiled with 0 error(s) and 0 warning(s),
the test can be reproduced by running:

  sbt "testFromTasty tests/run/eff-dependent.scala"

[allanrenucci]

This is the easiest way to reproduce but is it helpful for debugging? My experience is that when you run a test with vulpix and the compiler crashes then the exception is swallowed and I either need to look at the test log or run the compiler manually.

I often want to run the compiler manually outside vulpix and I would rather have the manual instructions. E.g:

> dotc -d tmp Foo.scala -some-options
> dotc Foo -classpath tmp -from-tasty -some-options

[nicolasstucki]

The issue is that there is no way at this point to know which are the inputs (class names) of the second script. I will try to come up with something more precise but for now, it is more important to emit a report that gives a correct way to reproduce the error.