Use FOT tools env var to override drift model root dir

[taldcroft]

Description

Per discussion in Slack ("implementation mismatch with the chandra_aca drift model" in #matlab_wg), this changes the name of the environment variable that is used to specify a drift model that is not in the Ska data tree.

Interface impacts

This also changes the definition of the environment variable. Previously it was the full path, but now it points to the root of the chandra_models repository (or like-structured directory tree) that has the model spec file. Since the original env var was never released and only used in testing this should not have any impact.

For reference the new root directory environment variable is THERMAL_MODELS_DIR_FOR_MATLAB_TOOLS_SW.

Testing

Updated the unit test to explicitly test the environment variable override (by monkeypatch) using a built-in version of the drift model spec file in the testing area.

Unit tests

• [x] Mac

Independent check of unit tests by Jean

• [x] Linux

Functional tests

No functional testing.

[jeanconn]

So for unit testing now, we'd run it with SKA set to a place that has SKA/data/chandra_models with the drift model and it will also patch to test against the copy that is in the module test data?

[jeanconn]

(Because previously I got out of this easy and had done my complementary testing with ACA_DRIFT_MODEL_PATH set explicitly. Now I just set up a test SKA/data with the new chandra_models so that the SKA version of the unit tests will pass).

[taldcroft]

So for unit testing now, we'd run it with SKA set to a place that has SKA/data/chandra_models with the drift model and it will also patch to test against the copy that is in the module test data?

Correct, it tests both code paths in the unit test.