The test_flags expansion contains variant-specific resmoke.py options including an alternate storage engine to use and additional tags to exclude. burn_in_tests.py should include the test_flags expansion in its resmoke.py invocation to ensure the task definitions it runs exactly match how those tasks would run on the specified build variant.

For example, invoking burn_in_tests.py with --buildVariant=linux-64-ephemeralForTest should cause resmoke.py to run with the ephemeralForTest storage engine and ignored any new/modified tests that require journaling or persistence.

- name: linux-64-ephemeralForTest
  display_name: Linux (ephemeralForTest)
  ...
  expansions: 
    test_flags: --storageEngine=ephemeralForTest --excludeWithAnyTags=requires_persistence,requires_fsync,SERVER-21420,SERVER-21658,requires_journaling
    ...