Fix s3 using IAM credentials
Fix s3 using IAM credentials

- pass `salt.utils.aws.IROLE_CODE` as the access_key and secret_key
  to `salt.utils.aws.sig4` so that sig4 grabs the full IAM
  credentials when it calls `creds`

saltstack/salt,saltstack/salt,saltstack/salt,saltstack/salt,saltstack/salt