Move jclouds-chef to the main jclouds repo

This pull request merges the providers in the jclouds-chef repo into the main jclouds one. The providers are just copied from there without changes. The change summary is:

* Copied the jclouds-chef providers to the *apis/chef* and *providers/enterprise-chef* folders.
* Changed their parent pom to *jclouds-project*, and updated the *relativePath* property accordingly.
* Changed the *jclouds-project/pom.xml* to fix a conflict in the *duplicate class finder* plugin between jclouds-core test-jar and the scriptbuilder test-jar. This didn't appear before because no other project included both test jars.

After this PR is merged we should edit the README of the jclouds-chef repo and make it clear it is now merged into the main one, but keep the existing repo for reference and older versions bugfixing.

And as a minor note, the *compute* folder in the jclouds-chef repo has not been migrated. It contained just some example tests that integrate chef with the compute service, but the feature is already covered in the existing chef live tests. Also the tests in there are basically a copy of the contents in the *chef-basics* project in the *jclouds-examples* repo. It makes no sense to have them as tests there (they also add *jclouds-all* as a dependency, which makes no sense), so we can safely get rid of them and keep the chef examples instead.

This was discussed in the dev@ mailing list, so @everett-toews Feel free to merge this PR before cutting the 1.8.0 release (and then forget about releasing the jclouds-chef repo) if you want.