Merge remote-tracking branch 'remotes/ericb/tags/pull-bitmaps-2020-06-09' into staging

bitmaps patches for 2020-06-09

- documenation fix
- various improvements to qcow2.py program used in iotests

# gpg: Signature made Tue 09 Jun 2020 21:50:35 BST
# gpg:                using RSA key 71C2CC22B1C4602927D2F3AAA7A16B4A2527436A
# gpg: Good signature from "Eric Blake <eblake@redhat.com>" [full]
# gpg:                 aka "Eric Blake (Free Software Programmer) <ebb9@byu.net>" [full]
# gpg:                 aka "[jpeg image of size 6874]" [full]
# Primary key fingerprint: 71C2 CC22 B1C4 6029 27D2  F3AA A7A1 6B4A 2527 436A

* remotes/ericb/tags/pull-bitmaps-2020-06-09:
  iotests: Fix 291 across more file systems
  qcow2_format.py: dump bitmaps header extension
  qcow2: QcowHeaderExtension print names for extension magics
  qcow2_format: refactor QcowHeaderExtension as a subclass of Qcow2Struct
  qcow2_format.py: QcowHeaderExtension: add dump method
  qcow2_format.py: add field-formatting class
  qcow2_format.py: separate generic functionality of structure classes
  qcow2_format.py: use strings to specify c-type of struct fields
  qcow2_format.py: use modern string formatting
  qcow2_format.py: use tuples instead of lists for fields
  qcow2_format.py: drop new line printing at end of dump()
  qcow2.py: move qcow2 format classes to separate module
  qcow2.py: add licensing blurb
  qcow2.py: python style fixes
  qemu-img: Fix doc typo for 'bitmap' subcommand

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