image-fuzzer: Generator of fuzzed qcow2 images

The layout submodule of the qcow2 package creates a random valid image,
randomly selects some amount of its fields, fuzzes them and write the fuzzed
image to the file. Fuzzing process can be controlled by an external
configuration.

Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Maria Kustova <maria.k@catit.be>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
