Merge remote-tracking branch 'remotes/armbru/tags/pull-qapi-2019-06-12' into staging

QAPI patches for 2019-06-12

# gpg: Signature made Wed 12 Jun 2019 17:44:50 BST
# gpg:                using RSA key 354BC8B3D7EB2A6B68674E5F3870B400EB918653
# gpg:                issuer "armbru@redhat.com"
# gpg: Good signature from "Markus Armbruster <armbru@redhat.com>" [full]
# gpg:                 aka "Markus Armbruster <armbru@pond.sub.org>" [full]
# Primary key fingerprint: 354B C8B3 D7EB 2A6B 6867  4E5F 3870 B400 EB91 8653

* remotes/armbru/tags/pull-qapi-2019-06-12:
  qapi: Simplify how QAPIDoc implements its state machine
  file-posix: Add dynamic-auto-read-only QAPI feature
  qapi: Allow documentation for features
  qapi: Disentangle QAPIDoc code
  tests/qapi-schema: Error case tests for features in structs
  tests/qapi-schema: Test for good feature lists in structs
  qapi: Add feature flags to struct types
  block/gluster: update .help of BLOCK_OPT_PREALLOC option
  block/file-posix: update .help of BLOCK_OPT_PREALLOC option
  qapi/block-core: update documentation of preallocation parameter
  qdev: Delete unused LostTickPolicy "merge"

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