Merge remote-tracking branch 'remotes/maxreitz/tags/pull-block-2019-11-26' into staging

Block patches for 4.2.0-rc3:
- Fix for shared storage migration with persistent dirty bitmaps

# gpg: Signature made Tue 26 Nov 2019 13:27:32 GMT
# gpg:                using RSA key 91BEB60A30DB3E8857D11829F407DB0061D5CF40
# gpg:                issuer "mreitz@redhat.com"
# gpg: Good signature from "Max Reitz <mreitz@redhat.com>" [full]
# Primary key fingerprint: 91BE B60A 30DB 3E88 57D1  1829 F407 DB00 61D5 CF40

* remotes/maxreitz/tags/pull-block-2019-11-26:
  iotests: add new test cases to bitmap migration
  block/qcow2-bitmap: fix bitmap migration

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