append cookbooks-local to cookbook path

[HACKISH] for testing on cookbooks you can proceed like this:

* put the cookbook (via git?) inside cookbooks-local/XXX
* any code change to the cookboo is applied on the next provisioning
* remove the cookbook from vendor/cookbooks/XXX if you want to get rid
  of warnings
* once finshed, commit and push

still seems awkward but don't have a better solution for now. ;)