CreateMetaDataBulk does not require unique metadata

This was found while testing #867 (closed), but is a separate issue since this is unrelated to the index attribute:

meta = {
    "name": "hello",
    "type": "text",
    "value": "blah",
}
cli.request('CreateMetaDataBulk', id=ELEMENT_ID, body={
    "metadata_list": [
        meta,
        meta
    ]
}

This should fail, since a unique name/type/value combo is required. If #867 (closed) gets fixed, we might end up with duplicates in the database since there is no DB constraint.