MINOR: cli: add a new keyword dump function

MINOR: cli: add a new keyword dump function

New function cli_list_keywords() scans the list of registered CLI keywords
and dumps them on stdout. It's now called from dump_registered_keywords()
for the class "cli".

Some keywords are valid for the master, they'll be suffixed with
"[MASTER]". Others are valid for the worker, they'll have "[WORKER]".
Those accessible only in expert mode will show "[EXPERT]" and the
experimental ones will show "[EXPERIM]".