argparse is nicer to use than getopt, and gives us --help almost for
free.
Signed-off-by: NMarkus Armbruster <armbru@redhat.com>
Message-Id: <20180211093607.27351-10-armbru@redhat.com>
Reviewed-by: NEric Blake <eblake@redhat.com>
Reviewed-by: NMarc-André Lureau <marcandre.lureau@redhat.com>
[eblake: Fix --output-dir editing accident]
Signed-off-by: NEric Blake <eblake@redhat.com>