blockjob: Update description of the 'device' field in the QMP API

- "type":     Job type (json-string; "stream" for image streaming

                                     "commit" for block commit)

- "device":   Device name (json-string)

- "device":   Job identifier. Originally the device name but other

              values are allowed since QEMU 2.7 (json-string)

- "len":      Maximum progress value (json-int)

- "offset":   Current progress value (json-int)

              On success this is equal to len.

- "type":     Job type (json-string; "stream" for image streaming

                                     "commit" for block commit)

- "device":   Device name (json-string)

- "device":   Job identifier. Originally the device name but other

              values are allowed since QEMU 2.7 (json-string)

- "len":      Maximum progress value (json-int)

- "offset":   Current progress value (json-int)

              On success this is equal to len.

Data:

- "device": device name (json-string)

- "device": Job identifier. Originally the device name but other

            values are allowed since QEMU 2.7 (json-string)

- "operation": I/O operation (json-string, "read" or "write")

- "action": action that has been taken, it's one of the following (json-string):

    "ignore": error has been ignored, the job may fail later

- "type":     Job type (json-string; "stream" for image streaming

                                     "commit" for block commit)

- "device":   Device name (json-string)

- "device":   Job identifier. Originally the device name but other

              values are allowed since QEMU 2.7 (json-string)

- "len":      Maximum progress value (json-int)

- "offset":   Current progress value (json-int)

              On success this is equal to len.

#

# @type: the job type ('stream' for image streaming)

#

# @device: the block device name

# @device: The job identifier. Originally the device name but other

#          values are allowed since QEMU 2.7

#

# @len: the maximum progress value

#

#

# Throttling can be disabled by setting the speed to 0.

#

# @device: the device name

# @device: The job identifier. This used to be a device name (hence

#          the name of the parameter), but since QEMU 2.7 it can have

#          other values.

#

# @speed:  the maximum speed, in bytes per second, or 0 for unlimited.

#          Defaults to 0.

# operation can be started at a later time to finish copying all data from the

# backing file.

#

# @device: the device name

# @device: The job identifier. This used to be a device name (hence

#          the name of the parameter), but since QEMU 2.7 it can have

#          other values.

#

# @force: #optional whether to allow cancellation of a paused job (default

#         false).  Since 1.3.

# the operation is actually paused.  Cancelling a paused job automatically

# resumes it.

#

# @device: the device name

# @device: The job identifier. This used to be a device name (hence

#          the name of the parameter), but since QEMU 2.7 it can have

#          other values.

#

# Returns: Nothing on success

#          If no background operation is active on this device, DeviceNotActive

#

# This command also clears the error status of the job.

#

# @device: the device name

# @device: The job identifier. This used to be a device name (hence

#          the name of the parameter), but since QEMU 2.7 it can have

#          other values.

#

# Returns: Nothing on success

#          If no background operation is active on this device, DeviceNotActive

#

# A cancelled or paused job cannot be completed.

#

# @device: the device name

# @device: The job identifier. This used to be a device name (hence

#          the name of the parameter), but since QEMU 2.7 it can have

#          other values.

#

# Returns: Nothing on success

#          If no background operation is active on this device, DeviceNotActive

#

# @type: job type

#

# @device: device name

# @device: The job identifier. Originally the device name but other

#          values are allowed since QEMU 2.7

#

# @len: maximum progress value

#

#

# @type: job type

#

# @device: device name

# @device: The job identifier. Originally the device name but other

#          values are allowed since QEMU 2.7

#

# @len: maximum progress value

#

#

# Emitted when a block job encounters an error

#

# @device: device name

# @device: The job identifier. Originally the device name but other

#          values are allowed since QEMU 2.7

#

# @operation: I/O operation

#

#

# @type: job type

#

# @device: device name

# @device: The job identifier. Originally the device name but other

#          values are allowed since QEMU 2.7

#

# @len: maximum progress value

#