ceph_argparse: add _daemon versions of argparse calls

mon needs to call argparse for a couple of -- options, and the
argparse_witharg routines were attempting to cerr/exit on missing
arguments.  This is appropriate for the CLI usage, but not the daemon
usage.  Add a 'cli' flag that can be set false for the daemon usage
(and cause the parsing routine to return false instead of exit).

The daemon's parsing code due for a rewrite soon.

Signed-off-by: Dan Mick <dan.mick@inktank.com>
Reviewed-by: Joao Eduardo Luis <joao.luis@inktank.com>
mon: Use _daemon version of argparse functions

Allow argparse functions to fail if no argument given by using
special versions that avoid the default CLI behavior of "cerr/exit"

Fixes: #4678
Signed-off-by: Dan Mick <dan.mick@inktank.com>
Reviewed-by: Joao Eduardo Luis <joao.luis@inktank.com>