breaking apart selenium files that take longer than 2 minutes to run

fixes CNVS-15690

test plan:
- run the following tests to ensure they pass
- /spec/selenium/assignments_spec.rb
- /spec/selenium/assignments_student_spec.rb
- /spec/selenium/assignments_group_spec.rb
- /spec/selenium/assignments_spec.rb
- /spec/selenium/assignments_overrides_spec.rb
- /spec/selenium/assignments_spec.rb
- /spec/selenium/submission_types_spec.rb
- /spec/selenium/assignments_observer_spec.rb
- /spec/selenium/outcome_spec.rb
- /spec/selenium/outcome_student_spec.rb
- /spec/selenium/outcome_teacher_spec.rb
- /spec/selenium/eportfolios_spec.rb
- /spec/selenium/assignments_content_spec.rb
- /spec/selenium/account_admin_outcomes_spec.rb
- /spec/selenium/state_outcomes_spec.rb

Change-Id: I49993cc7ec6c2f9152bea531c658c34acb989c84
Reviewed-on: https://gerrit.instructure.com/43557
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Mike Nomitch <mnomitch@instructure.com>
Product-Review: Matt Berns <mberns@instructure.com>
QA-Review: Matt Berns <mberns@instructure.com>