metadata.rb should be compiled into metadata.json before uploading

All dependencies should have their metadata.rb compiled into metadata.json if a metadata.json file is not present before uploading to a Chef Server.

Reference tickets on why:
* https://tickets.opscode.com/browse/CHEF-4811
* https://tickets.opscode.com/browse/CHEF-4810
* https://github.com/berkshelf/berkshelf/pull/923