Switch from api.berkshelf.com to supermarket

Currently `kitchen converge` fails to download cookbooks dependencies:
```
-----> Converging <server-ubuntu-1204>...
       Preparing files for transfer
       Resolving cookbook dependencies with Berkshelf 3.1.3...
E, [2014-08-16T19:08:41.260563 #93977] ERROR -- : Actor crashed!
Berkshelf::CommunitySiteError: An unexpected error occurred retrieving 'java' (1.25.0) from the cookbook site at ''.
	/Users/user/.rbenv/versions/2.1.1/lib/ruby/gems/2.1.0/gems/berkshelf-3.1.3/lib/berkshelf/community_rest.rb:123:in `find'
	/Users/user/.rbenv/versions/2.1.1/lib/ruby/gems/2.1.0/gems/berkshelf-3.1.3/lib/berkshelf/community_rest.rb:100:in `download'
	/Users/user/.rbenv/versions/2.1.1/lib/ruby/gems/2.1.0/gems/berkshelf-3.1.3/lib/berkshelf/downloader.rb:53:in `try_download'
```

Switch to supermarket helps and it's also recommended by Chef.