Replace spec tests on issue unit tests

This fixes the issue_tests https://github.com/codetriage/codetriage/issues/208.
More fixes to come on:
* test/unit/repo_subscriptions_test.rb
* test/functional/pages_controller_test.rb
* test/functional/repo_subscriptions_controller_test.rb

Just wanna se what you think about this initial one. 
review @schneems