Don't load tasks several times in specs

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.

spec/rails_helper.rb

@@ -12,6 +12,7 @@ require 'capybara/rails'
 require 'capybara/rspec'
 require 'selenium/webdriver'
 
+Rails.application.load_tasks
 I18n.default_locale = :en
 
 include Warden::Test::Helpers