Merge remote-tracking branch 'remotes/kevin/tags/for-upstream' into staging

Merge remote-tracking branch 'remotes/kevin/tags/for-upstream' into staging

Block layer patches:

- qcow2 cache option default changes (Linux: 32 MB maximum, limited by
  whatever cache size can be made use of with the specific image;
  default cache-clean-interval of 10 minutes)
- reopen: Allow specifying unchanged child node references, and changing
  a few generic options (discard, detect-zeroes)
- Fix werror/rerror defaults for -device drive=<node-name>
- Test case fixes

# gpg: Signature made Mon 01 Oct 2018 18:17:35 BST
# gpg:                using RSA key 7F09B272C88F2FD6
# gpg: Good signature from "Kevin Wolf <kwolf@redhat.com>"
# Primary key fingerprint: DC3D EB15 9A9A F95D 3D74  56FE 7F09 B272 C88F 2FD6

* remotes/kevin/tags/for-upstream: (23 commits)
  tests/test-bdrv-drain: Fix too late qemu_event_reset()
  test-replication: Lock AioContext around blk_unref()
  qcow2: Fix cache-clean-interval documentation
  block-backend: Set werror/rerror defaults in blk_new()
  qcow2: Explicit number replaced by a constant
  qcow2: Set the default cache-clean-interval to 10 minutes
  qcow2: Resize the cache upon image resizing
  qcow2: Increase the default upper limit on the L2 cache size
  qcow2: Assign the L2 cache relatively to the image size
  qcow2: Avoid duplication in setting the refcount cache size
  qcow2: Make sizes more humanly readable
  include: Add a lookup table of sizes
  qcow2: Options' documentation fixes
  block: Allow changing 'detect-zeroes' on reopen
  block: Allow changing 'discard' on reopen
  file-posix: Forbid trying to change unsupported options during reopen
  block: Forbid trying to change unsupported options during reopen
  block: Allow child references on reopen
  block: Don't look for child references in append_open_options()
  block: Remove child references from bs->{options,explicit_options}
  ...

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