Merge remote-tracking branch 'remotes/maxreitz/tags/pull-block-2018-03-26' into staging

Merge remote-tracking branch 'remotes/maxreitz/tags/pull-block-2018-03-26' into staging

A fix for dirty bitmap migration through shared storage, and a VMDK
patch keeping us from creating too large extents.

# gpg: Signature made Mon 26 Mar 2018 21:17:05 BST
# 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

* remotes/maxreitz/tags/pull-block-2018-03-26:
  vmdk: return ERROR when cluster sector is larger than vmdk limitation
  iotests: enable shared migration cases in 169
  qcow2: fix bitmaps loading when bitmaps already exist
  qcow2-bitmap: add qcow2_reopen_bitmaps_rw_hint()

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>