Merge remote-tracking branch 'remotes/qmp-unstable/queue/qmp' into staging

Merge remote-tracking branch 'remotes/qmp-unstable/queue/qmp' into staging

* remotes/qmp-unstable/queue/qmp: (38 commits)
  Revert "qapi: Clean up superfluous null check in qapi_dealloc_type_str()"
  qapi: Document optional arguments' backwards compatibility
  qmp: use valid JSON in transaction example
  qmp: Don't use error_is_set() to suppress additional errors
  dump: Drop pointless error_is_set(), DumpState member errp
  qemu-option: Clean up fragile use of error_is_set()
  qga: Drop superfluous error_is_set()
  qga: Clean up fragile use of error_is_set()
  qapi: Clean up fragile use of error_is_set()
  tests/qapi-schema: Drop superfluous error_is_set()
  qapi: Drop redundant, unclean error_is_set()
  hmp: Guard against misuse of hmp_handle_error()
  qga: Use return values instead of error_is_set(errp)
  error: Consistently name Error ** objects errp, and not err
  qmp: Consistently name Error ** objects errp, and not err
  qga: Consistently name Error ** objects errp, and not err
  qmp hmp: Consistently name Error * objects err, and not errp
  pci-assign: assigned_initfn(): set monitor error in common error handler
  pci-assign: propagate errors from assign_intx()
  pci-assign: propagate errors from assign_device()
  ...

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