Change box name to vector in meta json

Change box name to vector in meta json

outputmetadata box name was single string, but needs to change to
handle yolo models.(multiple names)
`before`
"box" :
    {
        "name" : "some name",
        ...
    }
`after`
"box" :
    {
        "name" : ["some name"],
        ...
    }

Change-Id: Ia76001c2670c0a1fae272c31ba56dfc0cbc591de
Signed-off-by: Kwanghoon Son <k.son@samsung.com>