Fix unavailable period less than 24 hours

[joseph-robertson]

Pull Request Description

Checklist:

• Update schedules.rb's set_unavailable_periods method
  • change "outage" to "unavailable"
  • refactor all the duplicate code
• Add simple schedule unit tests for 12/14 20 - 12/15 6

Checklist

Not all may apply:

• Schematron validator (EPvalidator.xml) has been updated
• Sample files have been added/updated (openstudio tasks.rb update_hpxmls)
• Tests have been added/updated (e.g., HPXMLtoOpenStudio/tests/test*.rb and/or workflow/tests/test*.rb)
• Documentation has been updated
• Changelog has been updated
• openstudio tasks.rb update_measures has been run
• No unexpected changes to simulation results of sample files

[shorowit]

No changes to results, nice code cleanup, new tests. LGTM, thanks @joseph-robertson!