Merge remote-tracking branch 'mreitz/tags/pull-block-2017-09-26' into queue-block

Block patches

# gpg: Signature made Tue Sep 26 15:01:00 2017 CEST
# gpg:                using RSA key F407DB0061D5CF40
# gpg: Good signature from "Max Reitz <mreitz@redhat.com>"
# Primary key fingerprint: 91BE B60A 30DB 3E88 57D1  1829 F407 DB00 61D5 CF40

* mreitz/tags/pull-block-2017-09-26:
  block/qcow2-bitmap: fix use of uninitialized pointer
  qemu-iotests: add shrinking image test
  qcow2: add shrink image support
  qcow2: add qcow2_cache_discard
  qemu-img: add --shrink flag for resize

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