Merge remote-tracking branch 'stefanha/block' into staging

# By Wenchao Xia (5) and others
# Via Stefan Hajnoczi
* stefanha/block:
  coroutine: stop using AioContext in CoQueue
  coroutine: protect global pool with a mutex
  qemu-iotests: Try creating huge qcow2 image
  qcow2.py: Subcommand for changing header fields
  qemu-io: Fix 'map' output
  blockdev: Rename BlockdevAction -> TransactionAction
  block: make all steps in qmp_transaction() as callback
  block: package rollback code in qmp_transaction()
  block: package committing code in qmp_transaction()
  block: move input parsing code in qmp_transaction()
  block: package preparation code in qmp_transaction()

Message-id: 1369405947[email protected]
Signed-off-by: Anthony Liguori <[email protected]>