qemu-img should allow resizing image with snapshots

Currently it's not possible to resize a disk image with qemu-img if image in question has snapshots associated. I'm not entirely sure this is technically possible but if it is, it would be really nice to support that.

$ qemu-img --version
qemu-img version 2.4.1 (qemu-2.4.1-8.fc23), Copyright (c) 2004-2008 Fabrice Bellard