ceph, MonCommands.h:  code format/help format tweaks

Signed-off-by: Dan Mick <dan.mick@inktank.com>
ceph: first cut at --completion

Factor out parsing JSON to sigdict; use from both main and completion
Currently invoking from bash completion with

        n=${#COMP_WORDS} # length
        # invoke with all but first word
        COMPREPLY=( $(ceph --completion "${COMP_WORDS[@]:1:$n}") )

Not handling --arg and not dealing correctly with cursor-on-last-letter
vs. cursor-on-space

Signed-off-by: Dan Mick <dan.mick@inktank.com>