The patch allows to provide a pattern file for write
command. There was no similar ability before.

Signed-off-by: Denis Plotnikov <dplotnikov@virtuozzo.com>
Message-id: 20190820164616.4072-1-dplotnikov@virtuozzo.com
Reviewed-by: Eric Blake <eblake@redhat.com>
[mreitz: Keep optstring in alphabetical order]
Signed-off-by: Max Reitz <mreitz@redhat.com>