More RSpec 3 deprecations
Fix for intermittent failure in app spec

RSpec 3 tightens up about using doubles after they've been reset at the
end of a test's usage.

Shoes holds onto a list of apps that have been created, and this class
level state was catching some doubles that persisted across multiple
test runs. When the app_spec happened to try to delete some of those
doubles, RSpec rightly complained.

Now at least in app_spec we clear out the app list every time after our
tests.