[COOK-3534][COOK-3535] Add virtualization system to default tags and fix...

... EnvVars

Also add a kitchen scenario for a node to test setting these fixes.

Note that the EnvVars fix is also from [PR 47](https://github.com/opscode-cookbooks/jenkins/pull/47). Minitests may be added once [PR 55](https://github.com/opscode-cookbooks/jenkins/pull/55) is merged.