SI-7704 Fix partest's test category selection

My recent changes to command line parsing in 6090709 broke partest's
functionality of picking test categories (e. g. --pos or --run).

The breakage was caused because scala.tools.cmd._ stored the command
line options with the `--` prefix, but TestKinds.standardKinds did not.
Add some explicit return types to s.t.c._
Clean up ConsoleRunner, --> returns Boolean ...

... not Unit now.
Merge pull request #2785 from soc/SI-7704

SI-7704 Fix partest's test category selection