Merge remote-tracking branch 'mreitz/tags/pull-block-2018-04-03' into queue-block

A fix for preallocated truncation, a new iotest, and a fix to make the iotests work more comfortably on ppc64

# gpg: Signature made Tue Apr  3 17:40:57 2018 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-2018-04-03:
  iotests: Test abnormally large size in compressed cluster descriptor
  qemu-iotests: Use ppc64 qemu_arch on ppc64le host
  iotests: Test preallocated truncate of 2G image
  block/file-posix: Fix fully preallocated truncate

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