As `make test-tool` does not use gems, and no Rubygems stuffs is
needed, so moved such things to test/runner.rb. Also no longer
nees `--test-target-dir` option.
tool/test/runner.rb had been copied from test/runner.rb.
test/runner.rb was for `make test-all`, and tool/test/runner.rb was for
`make test-testframework` and `make test-tool`.
But I want to avoid the code clones.
This change makes tool/test/runner.rb support --test-target-dir option
which allows tool/test/runner.rb to run `make test-all`.
Now we can remove test/runner.rb.
