Merge remote-tracking branch 'remotes/stefanha/tags/block-pull-request' into staging

Merge remote-tracking branch 'remotes/stefanha/tags/block-pull-request' into staging

Pull request

# gpg: Signature made Fri 10 May 2019 14:02:22 BST
# gpg:                using RSA key 8695A8BFD3F97CDAAC35775A9CA4ABB381AB73C8
# gpg: Good signature from "Stefan Hajnoczi <stefanha@redhat.com>" [full]
# gpg:                 aka "Stefan Hajnoczi <stefanha@gmail.com>" [full]
# Primary key fingerprint: 8695 A8BF D3F9 7CDA AC35  775A 9CA4 ABB3 81AB 73C8

* remotes/stefanha/tags/block-pull-request:
  docs: add Security chapter to the documentation
  docs: add Secure Coding Practices to developer docs
  aio-posix: ensure poll mode is left when aio_notify is called
  block/io.c: fix for the allocation failure
  block: Add coroutine_fn to bdrv_check_co_entry
  util/readline: Add braces to fix checkpatch errors
  util: readline: replace tab indent by four spaces to fix checkpatch errors
  util/readline: add a space to fix errors by checkpatch tool

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