Update to RSpec 3

Sorry for jumbo PR. This is sorely needed for some upcoming work.

Used transpec to update most of the files. The major exceptions are covering the changes to `pending`. Generally, I use `pending` if an `:if` was supplied, and `skip` if a filter was given or `pending` was not given a block.

\cc @opscode/client-engineers 
what a great expectation :+1: