Completely move to Supermarket

This introduces some breaking changes. First, the defaults are all now
pointing at Supermarket. Additionally, the Supermarket worker now just
consumes the +universe.json+ endpoint instead of downloading thousands of
cookbooks for indexing.

We are currently seeing exceptionally high loads from users indexing the new
Supermarket site, so this would be a great patch to merge. It reduces
bandwidth and prevents the need to download every cookbook just to parse the
metadata.
Fix failing supermarket specs
Fix failing GitHub specs
Fix failing Supermarket worker specs
Remove all uses of "its" (RSpec deprecation)
Replace be_true with be_truthy (RSpec deprecation)
Change pending to skip (RSpec deprecation)
Change have(n).items to .size eq(n) (RSpec deprecated)
Remove unneeded test for the Supermarket URL
Use > instead of greater_than
Use a helper method to create a remote_cookbook
Stub celluloid objects with #wrapped_object
Install without development gems on CI
Merge pull request #151 from berkshelf/sethvargo/supermarket

Completely move to Supermarket