Fix box array to object in meta json

Fix box array to object in meta json

outputmetadata box object has array, but usage only accept 1 array
element. This change handle object instead array.
`before`
"box" : [
    {
        "name" : "some name",
        ...
    }
],
`after`
"box" :
    {
        "name" : "some name",
        ...
    }

Change-Id: If77d781a5f4bbf6beb7078e34edd5309f29a471e
Signed-off-by: Kwanghoon Son <k.son@samsung.com>