Change the io_test and io_test2 functions to take the cluster size of the image
and the number of test requests to issue. Tests are changed to specify a
cluster size (usually 4k), but expected test results stay the same for now
(apart from qemu-img printing the cluster size now).

Based on a patch written by Christoph Hellwig.
Signed-off-by: NKevin Wolf <kwolf@redhat.com>
Signed-off-by: NChristoph Hellwig <hch@lst.de>

Signed-off-by: NKevin Wolf <kwolf@redhat.com>
Signed-off-by: NChristoph Hellwig <hch@lst.de>

Blue Swirl notices that we were using the old FSF post address in the
license boilerplates.  Replace both the old and new address with links
to the gnu.org licenses homepage as suggested by Ben Pfaff.
Signed-off-by: NChristoph Hellwig <hch@lst.de>

Pretend that a non-implemented check is always successful and thus allow
various tests that were qcow2-specific before to be generic.
Signed-off-by: NChristoph Hellwig <hch@lst.de>
Reviewed-by: NKevin Wolf <kwolf@redhat.com>

Signed-off-by: NKevin Wolf <kwolf@redhat.com>