Add serverspec to gems
Install sample package
Add spec/integration/
Run integration test with serverspec
Remove minitest integration test
Update TESTING.md
Move unit tests to spec/unit/

Also, install fixtures to vendor/cookbooks, which is used by
ChefSpec by default.
Rename Rake task test:spec to test:unit
Remove .kitchen folder via `rake clobber`
Stop copying spec/ to fixtures

Finally separate fixtures from specs!
Merge pull request #14 from mlafeldt/serverspec

Integration testing with serverspec