Fix afn_single_zone_xx tests

Checklist:

• Fix failing afn_single_zone_ac.rb

• afn_single_zone_nv.osm is failing in 2.5.0

afn_single_zone_ac.rb is failing.

Test was added in https://github.com/NREL/OpenStudio-resources/pull/39

With current OpenStudio develop, run.log shows:

[16:01:23.770659 ERROR] Found error in state 'translator' with message ["std::bad_cast::/ruby/2.2.0/gems/openstudio-workflow-1.3.2/lib/openstudio/workflow/util/model.rb:66:in `translateModel'\n:/ruby/2.2.0/gems/openstudio-workflow-1.3.2/lib/openstudio/workflow/util/model.rb:66:in `translate_to_energyplus'\n:/ruby/2.2.0/gems/openstudio-workflow-1.3.2/lib/openstudio/workflow/jobs/run_translation.rb:54:in `perform'\n:/ruby/2.2.0/gems/openstudio-workflow-1.3.2/lib/openstudio/workflow/run.rb:261:in `step'\n:/ruby/2.2.0/gems/openstudio-workflow-1.3.2/lib/openstudio/workflow/run.rb:210:in `run'\n:/openstudio_cli.rb:821:in `execute'\n:/openstudio_cli.rb:620:in `execute'\n:/openstudio_cli.rb:1547:in `<main>'\neval:85:in `eval'\neval:85:in `require_embedded_absolute'\neval:70:in `block in require'\neval:64:in `each'\neval:64:in `require'\neval:2:in `<main>'"]}

afn_single_zone_nv.osm is failing too.

Start with afn_single_zone_ac.rb and afn_single_zone_nv.osm, then inspect the referenced run.log translator error with current OpenStudio develop. Compare the two failing cases and their existing test setup; done means both afn_single_zone tests run successfully without the reported translator failure.