Change the default to modern qcow2 as it's supported by all qemu
versions supported by libvirt and in fact 'qemu-img' already defaults to
the new format for a long time.
Some Unittests require changes to pass, now that version 1.1 is default.
Unittests like `qcow2-1.1.argv` may not be relevant anymore, but this
patch doesn't affect them.
Closes: https://gitlab.com/libvirt/libvirt/-/issues/602
Signed-off-by: Abhiram Tilak <atp.exp@gmail.com>
Reviewed-by: Peter Krempa <pkrempa@redhat.com>
