Merge remote-tracking branch 'remotes/maxreitz/tags/pull-block-2019-08-06' into staging

Block patches for 4.1.0-rc4:
- Fix the backup block job when using copy offloading
- Fix the mirror block job when using the write-blocking copy mode
- Fix incremental backups after the image has been grown with the
  respective bitmap attached to it

# gpg: Signature made Tue 06 Aug 2019 12:57:07 BST
# 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-2019-08-06:
  block/backup: disable copy_range for compressed backup
  iotests: Test unaligned blocking mirror write
  mirror: Only mirror granularity-aligned chunks
  iotests: Test incremental backup after truncation
  util/hbitmap: update orig_size on truncate
  iotests: Test backup job with two guest writes
  backup: Copy only dirty areas

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