We currently use a $PREPARE_SHELL macro to export all environment variables needed/expected by our test suite at runtime. Whenever a new environment variable needs to be added to a given buildvariant, not only do we need to update the axis with the new expansion variable, we must also update the macro to export this expansion as an environment variable.

This results in a somewhat hard to maintain Evergreen config, especially for newcomers to the project. We can further optimize some of these invocations by switching to using subprocess.exec instead of shell.exec and then setting either the include_expansions_in_env option or the add_expansions_to_env option to automatically set the appropriate environment variables.