Update Measure guide for 2.x measure tests

[jmarrec]

Transferred from NatLabRockies/OpenStudio#2614

http://nrel.github.io/OpenStudio-user-documentation/reference/measure_writing_guide/#putting-it-all-together-a-complete-measure-test-file

There may be other areas to update as well.

• measure test
• valid output variables
• relationship between measure display name, name, class name, and directory name

[jmarrec]

MiniTest::Unit::TestCase should be Minitest::Test.

It also uses the old deprecated Ruleset namespace.

    runner = OpenStudio::Ruleset::OSRunner.new

Should use Measure::OSRunner.new(workflow_json)

There's also MUCH older stuff like wf = OpenStudio::Runmanager::Workflow.new("modeltoidf->energypluspreprocess->energyplus") which is from OpenStudio 0.X...

[Sashadf1]

I noticed the "MiniTest::Unit::TestCase should be Minitest::Test" as well.