Have Jenkins run integration tests

This will bring vCloud Walker into line with all the other gems, where the main Jenkins job:

 - builds the project
 - runs the unit and any feature tests
 - runs the integration tests against Skyscape
 - if the version has changed and the above tests all pass, publishes the new version to RubyGems
Merge pull request #60 from alphagov/run-integration

[#65294218] Have Jenkins run integration tests