Add @ruby tag to Ruby scenarios.
Merge pull request #350 from trema/feature/cucumber_tagging

Add @ruby tag to Ruby scenarios.
cruise.rb runs only @critical tests to speed up Trema's test suite.

To run all tests, do "cruise.rb --all".
Merge pull request #351 from trema/feature/cruise_all

cruise.rb runs only @critical tests to speed up Trema's test suite.