Merge remote-tracking branch 'remotes/maxreitz/tags/pull-block-2020-02-06' into staging

Block patches:
- Drop BDRV_SECTOR_SIZE from qcow2
- Allow Python iotests to be added to the auto group
  (and add some)
- Fix for the backup job
- Fix memleak in bdrv_refresh_filename()
- Use GStrings in two places for greater efficiency (than manually
  handling string allocation)

# gpg: Signature made Thu 06 Feb 2020 12:50:14 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-2020-02-06:
  iotests: add test for backup-top failure on permission activation
  block/backup-top: fix failure path
  qcow2: Use BDRV_SECTOR_SIZE instead of the hardcoded value
  qcow2: Don't require aligned offsets in qcow2_co_copy_range_from()
  qcow2: Use bs->bl.request_alignment when updating an L1 entry
  qcow2: Tighten cluster_offset alignment assertions
  qcow2: Don't round the L1 table allocation up to the sector size
  iotests: Enable more tests in the 'auto' group to improve test coverage
  iotests: Skip Python-based tests if QEMU does not support virtio-blk
  iotests: Check for the availability of the required devices in 267 and 127
  iotests: Test 183 does not work on macOS and OpenBSD
  iotests: Test 041 only works on certain systems
  iotests: remove 'linux' from default supported platforms
  qcow2: Use a GString in report_unsupported_feature()
  block: fix memleaks in bdrv_refresh_filename
  block: Use a GString in bdrv_perm_names()
  qcow2: Assert that host cluster offsets fit in L2 table entries

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