Librarian: Vendor cookbooks into cookbooks/.  Berks: `which` debug.

Fix typo in Librarian resolver so that it installs vendored cookbooks
into kitchenplan's cookbooks directory, not the config directory.

Berks appears to be having problems finding its binary after it gets
installed by Bundler on the Travis systems.  On my Mac it just goes
into /usr/bin...
Use PATH environment for resolver binary path search.

Hopefully this will resolve the Berks binary pathing issue in Travis.