Function certify 

pub async fn certify<B: BlobBackend>(
    target: &B,
    config: &Config,
    metadata: &Config,
) -> Vec<Certified>

Run every leaf here against target and return one row per leaf.

config is the facts the gate can read for this target (collation=...); metadata is copied into every row, with test=blob::<leaf> added. A leaf is on only if the target passed and the positive control passed and every known-bad control failed.