Calling `load_tasks` in several files made rails load the tasks several
times, and so they were executed several times when called.
Since the milestone migration can't be executed twice in a row (it would
fail with duplicated ID records), loading the tasks several times made
the milestone migrations task specs fail.
This cop tries to avoid state leaking between examples. The fixes done on the code don't follow the suggested path, since the usage of `before(:all)` was not really useful. By using RSpec's `let` method we achieve same goals but with much better and readable tests.
Check Cop description at http://www.rubydoc.info/gems/rubocop-rspec/RuboCop/Cop/RSpec/BeforeAfterAll
