Add cucumber config file

Add a cucumber config file with a default profile that ignores tests
that are known to be failing and pretty formats the output.
Remove cucumber opts from Rakefile

Remove cucumber opts from Rakefile as they are now being provided by
.config/cucumber.yml
Make run_tests.sh run like jenkins.sh
Merge pull request #8 from alphagov/add-cucumber-config

Make run_tests.sh and jenkins.sh work the same way