qemu-img: fix --image-opts usage with dd command

The --image-opts flag can only be used to affect the parsing
of the source image. The target image has to be specified in
the traditional style regardless, since it needs to be passed
to the bdrv_create() API which does not support the new style
opts.

Reviewed-by: Fam Zheng <famz@redhat.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
Message-id: 20170515164712.6643-3-berrange@redhat.com
Signed-off-by: Max Reitz <mreitz@redhat.com>