[PATCH v2 4/4] pwclient: use argparse's error() function for bad input

[Finucane, Stephen]

> > This reduces the boilerplate we need and provides a more consistent help
> > output. e.g.:
> >
> >    $ pwclient update -s FOO -c 1337 314159 1234567
> >    usage: pwclient update [--help] [-h HASH] [-p PROJECT] [-c COMMIT-REF]
> >                           [-s STATE] [-a {yes,no}]
> >                           [ID [ID ...]]
> >    pwclient update: error: Declining update with COMMIT-REF on multiple
> IDs
> >
> > Signed-off-by: Brian Norris <computersforpeace at gmail.com>
> > ---
> > v2: new in this series, per Mike's suggestion
> 
> Yeah, this is a good improvement.
> 
> Reviewed-by: Stephen Finucane <stephen.finucane at intel.com>

Merged.