Refactor the testing code to be agnostic to the host land model

[glemieux]

The current implementation of the fates testing infrastructure assumes that the tests will be run within ctsm:

fates/testing/path_utils.py

Line 23 in f5bd625

cime_path = os.path.join(path_to_fates_root(), "../../cime")

Ideally this would be updated to be agnostic to the host land model or allow the tests to take the cime location as an argument.

[glemieux]

Whenever we change history output naming we break regression tests (typically the "all vars" test), which means we need to coordinate the updates across HLMs. E.g. #1252.

[ekluzek]

This sounds like a great idea.

I also think we should have a way to just have the code figure out what all the history variables are and turn them all on.