* Force tests to set ansible_python_interpreter.
This avoids use of interpreter discovery unless tests opt-in to using it.
Avoiding interpreter discovery helps avoid selecting the wrong interpreter for tests.
* Prevent use of global inventory in tests.
This will avoid issues with tests picking up global inventory
instead of using implicit localhost as intended.
* Require hosts to exist in inventory for tests.
This will prevent tests from unintentionally passing
when hosts are not found in inventory. Does not prevent
the use of implicit localhost.
