tools/testing/cxl: add mock output for the GET_HEALTH_INFO command

Add mocked health information for cxl_test memdevs. This allows
cxl-cli's 'list' command to display the canned health_info fields.

Cc: Dan Williams <dan.j.williams@intel.com>
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Signed-off-by: Vishal Verma <vishal.l.verma@intel.com>
Link: https://lore.kernel.org/r/20211018051251.2289112-1-vishal.l.verma@intel.com
Signed-off-by: Dan Williams <dan.j.williams@intel.com>