config: replace uses of deprecated io/ioutil
config: replace uses of deprecated io/ioutil

Signed-off-by: Sebastiaan van Stijn <64b2b6d12bfe4baae7dad3d018f8cbf6b0e7a044@gone.nl>

cloudflare/cfssl,cloudflare/cfssl,cloudflare/cfssl,cloudflare/cfssl