Rake tasks cookbook:test and cookbook:dev_test can be run against a chef repo.

Case 1: The cwd is a chef repo, strainer will be run on each cookbook in the folder cookbooks.
Case 2: The cwd is a cookbook repo, strainer will be run on this cookbook.
Case 3: The user uses the option "name" e.g "name=cookbook1,cookbook2", so strainer will be run on each cookbook mentioned in the option "name" only.
Use args.extras instead of ENV[names] for retrieving the names of the cookbooks.

Before rake cookbook:test name=cookbook1,cookbook2.
Now rake cookbook:test[cookbook1,cookbook2]
Merge pull request #1 from hipsnip-cookbooks/usable-also-in-a-chef-repo

Rake tasks cookbook:test and cookbook:dev_test can also be run against a chef repo or a subset of cookbooks