tools/testing/nvdimm: unit test clear-error commands

Validate command parsing in acpi_nfit_ctl for the clear error command.
This tests for a crash condition introduced by commit 4b27db7e


"acpi, nfit: add support for the _LSI, _LSR, and _LSW label methods".

Cc: Vishal Verma <vishal.l.verma@intel.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>