From: Dan Williams <dan.j.williams@intel.com>
Each md_message encapsulates a single command. A command includes an 'action'
member which describes what if any data comes after the action. Communication
with the monitor involves updating the active_cmd pointer and then writing to
mgr_pipe. Pass/fail status is returned via mon_pipe.
Signed-off-by: Dan Williams <dan.j.williams@intel.com>