Should help people dealing with #4570 and #3328 because packer copies
`floppy_files` to floppy without any error even if they exceed 1.44 MB
limit. `floppy_dirs`throws error about FAT size limit exceeded but
without mentioning that real issue is the floppy size limit:
```
Build 'qemu' errored: Error adding path virtio_iso to floppy: FAT FULL
```