Stop issuing a warning about Module::TimeoutError in specs
Stop issuing a warning about Module::TimeoutError in specs

The assumptions spec is used to make sure that no new models are taggable
and it does so by loading all constants and checking that no AR::Base
subclasses respond to `tagged_with`.  This has the side-effect of loading
a constant deprecated by ruby 2.3.x (`TimeoutError`) and issuing a
warning about it.  Instead of loading all constants, we can instead
load all descendants of AR::Base (see: http://api.rubyonrails.org/classes/ActiveSupport/DescendantsTracker.html#method-c-descendants)
and start from there - avoiding TimeoutError entirely.

alphagov/transition,alphagov/transition,alphagov/transition