[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>