Describe the issue:

Decreasing block image size requires --allow-shrink flag

2.7. Resizing a block device image:

	Given command can only be used to increase the image size
        rbd resize --image IMAGE_NAME --size SIZE
        rbd resize --image POOL_NAME/IMAGE_NAME --size SIZE

        #rbd create image1 --size 1024 --pool pool1						
	#rbd resize --image pool1/image1 --size 512
         rbd: shrinking an image is only allowed with the --allow-shrink flag