tools/testing/nvdimm: Populate dirty shutdown data

Allow the unit tests to verify the retrieval of the dirty shutdown
count via smart commands, and allow the driver-load-time retrieval of
the smart health payload to be simulated by nfit_test.

Reviewed-by: Keith Busch <keith.busch@intel.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>