Merge remote-tracking branch 'remotes/maxreitz/tags/pull-block-2019-09-03' into staging

Block patches:
- qemu-io now accepts a file to read a write pattern from
- Ensure that raw files have their first block allocated so we can probe
  the O_DIRECT alignment if necessary
- Various fixes

# gpg: Signature made Tue 03 Sep 2019 13:58:57 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-2019-09-03:
  iotests: Unify cache mode quoting
  tests/check-block: Skip iotests when sanitizers are enabled
  iotests: Check for enabled drivers before testing them
  iotests: Add -display none to the qemu options
  file-posix: fix request_alignment typo
  iotests: Disable 126 for flat vmdk subformats
  iotests: Disable 110 for vmdk.twoGbMaxExtentSparse
  iotests: Disable broken streamOptimized tests
  vmdk: Reject invalid compressed writes
  iotests: Keep testing broken relative extent paths
  vmdk: Use bdrv_dirname() for relative extent paths
  iotests: Fix _filter_img_create()
  iotests: Test allocate_first_block() with O_DIRECT
  block: posix: Always allocate the first block
  block: fix permission update in bdrv_replace_node
  qemu-io: add pattern file for write command

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