Remove "growable" option from the "open" command and from the qemu-io
command line. qemu-io is about to be converted to BlockBackend which
will make sure that no request exceeds the image size, so the only way
to keep "growable" would be to use BlockBackend if it is not given and
to directly access the BDS if it is.

qemu-io is a debugging tool, therefore removing a rarely used option
will have only a very small impact, if any. There was only one
qemu-iotest which used the option; since it is not critical, this patch
just removes it.
Signed-off-by: NMax Reitz <mreitz@redhat.com>
Reviewed-by: NEric Blake <eblake@redhat.com>
Message-id: 1423162705-32065-13-git-send-email-mreitz@redhat.com
Signed-off-by: NStefan Hajnoczi <stefanha@redhat.com>