test_dynamodb_runner: use the ioutil wrapped version of IsNotExist (#612)
test_dynamodb_runner: use the ioutil wrapped version of IsNotExist (#612)

Because ioutil.Stat returns a wrapped error.
keybase/kbfs,keybase/client,keybase/client,keybase/client,keybase/client,keybase/client,keybase/client,keybase/client,keybase/client,keybase/kbfs,keybase/client,keybase/kbfs,keybase/client,keybase/client,keybase/kbfs,keybase/client