Merge remote-tracking branch 'remotes/armbru/tags/pull-qapi-2018-06-22' into staging

QAPI patches for 2018-06-22

# gpg: Signature made Fri 22 Jun 2018 15:36:22 BST
# gpg:                using RSA key 3870B400EB918653
# gpg: Good signature from "Markus Armbruster <armbru@redhat.com>"
# gpg:                 aka "Markus Armbruster <armbru@pond.sub.org>"
# Primary key fingerprint: 354B C8B3 D7EB 2A6B 6867  4E5F 3870 B400 EB91 8653

* remotes/armbru/tags/pull-qapi-2018-06-22:
  MAINTAINERS: Update QAPI stanza for commit fb0bc835
  qapi/introspect: Eliminate pointless variable in .visit_end()
  Revert commit d4e5ec87
  qapi: Open files with encoding='utf-8'
  qapi: remove empty flat union branches and types
  qapi: allow empty branches in flat unions
  tests: Add QDict clone-flatten test
  qdict: Make qdict_flatten() shallow-clone-friendly
  qapi/events: generate event enum in main module
  qapi/visit: remove useless prefix argument

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