[Docker] Set test certificate file modes
[Docker] Set test certificate file modes

* To be able to run tests as non-root user, make sure test certs
  (even private ones) are readable.

bmwcarit/joynr,bmwcarit/joynr,bmwcarit/joynr,bmwcarit/joynr,bmwcarit/joynr,bmwcarit/joynr,bmwcarit/joynr,bmwcarit/joynr,bmwcarit/joynr