Merge remote-tracking branch 'kwolf/for-anthony' into staging

* kwolf/for-anthony:
  fdc-test: introduced qtest no_media_on_start and cmos qtest for floppy
  fdc: fix media detection
  fdc: floppy drive should be visible after start without media
  qemu-iotests: mark 035 qcow2-only
  qcow2: Check qcow2_alloc_clusters_at() return value
  sheepdog: use heap instead of stack for BDRVSheepdogState
  sheepdog: return -errno on error
  sheepdog: mark image as snapshot when tag is specified
  qemu-img: Explain how rebase operation can be used to perform a 'diff' operation.
  qcow2: don't leak buffer for unexpected qcow_version in header