qmp-commands: move 'block_resize' doc to schema

<- { "return": { "status": "active", "completed": 1024000,

                 "total": 2048000 } }

block_resize

------------

Resize a block image while a guest is running.

Arguments:

- "device": the device's ID, must be unique (json-string)

- "node-name": the node name in the block driver state graph (json-string)

- "size": new size

Example:

-> { "execute": "block_resize", "arguments": { "device": "scratch", "size": 1073741824 } }

<- { "return": {} }

block-stream

------------

#          If @device is not a valid block device, DeviceNotFound

#

# Since: 0.14.0

#

# Example:

#

# -> { "execute": "block_resize",

#      "arguments": { "device": "scratch", "size": 1073741824 } }

# <- { "return": {} }

#

##

{ 'command': 'block_resize', 'data': { '*device': 'str',

                                       '*node-name': 'str',