[C++] Fixed PublicationManagerTest.add_onChangeWithMinInterval
[C++] Fixed PublicationManagerTest.add_onChangeWithMinInterval

* Double timing values in add_onChangeWithMinInterval() to
  avoid problems on slow systems

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