rails3: fix for erubis issues and quizzes controller specs

things fixed:
  - erubis is in actionpack gemspec in rails3, so we don't need it in the gemfile
  - don't directly initialize a SafeBuffer, and instead initialize OutputBuffer
  - Fix comparison of hash with indifferent access in quizzes spec
  - plugins in rails3 aren't loaded in init.rb so rails_xss is still being
    loaded in rails3. However we have parts of the code that actually reference
    rails_xss classes directly so we want to keep the RailsXss::Erubis constant
    defined in erubis.rb. However we don't want to actually monkey patch
    the activesupport or string methods anymore for xss (rails3 takes care of
    this for us)

Change-Id: I327bf042dfa7dcedd39acb463eda1420d3dbd98c
Reviewed-on: https://gerrit.instructure.com/30108
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Cameron Matheson <cameron@instructure.com>
Product-Review: Derek DeVries <ddevries@instructure.com>
QA-Review: Derek DeVries <ddevries@instructure.com>