block: Add synchronous wrapper for bdrv_co_is_allocated_above

There's no synchronous wrapper for bdrv_co_is_allocated_above function
so it's not possible to check for sector allocation in an image with
a backing file.
qemu-img: Add "Quiet mode" option

There can be a need to turn output to stdout off. This patch adds a -q option
that enable "Quiet mode". In Quiet mode, only errors are printed out.

Signed-off-by: Miroslav Rezanina <mrezanin@redhat.com>
This patch adds new qemu-img subcommand that compares content of two disk
images.

Signed-off-by: Miroslav Rezanina <mrezanin@redhat.com>