Fix race-condition between user-data and library.bash

When stark or whitewalker is started, the CA certificate is injected using user-data. `rc.local` might start the experiments earlier than user-data was able to inject the CA certificate and at the first `log` command (influxdb connection over TLS), things fall apart.

- Implement a flag to see if the CA certificate was added already
- Only start stark.bash/whitewalker.bash when the flag is present
- If the flag is not present, random backoff and wait (until a timeout?)