Add options to leave containers running and skip tests

Problem

Sometimes I want to re-run a test via gitlab-qa, or inspect GitLab after the tests have finished, or I want to easily set up an orchestrated environment and don't want to have to mess around with my GDK setup. And I want to be able to do that without having to wait for all the tests in a scenario to complete.

Proposal

• Add a --[no-]teardown option
  • --no-teardown: leave the containers running once a scenario is complete
  • --teardown: teardown the containers
• Add a --[no-]tests option
  • --no-tests: start the containers but skip the tests
  • --tests: run the tests against running containers