[C++] Added RadixTreeTest to check longestMatch() does not return wrong node
[C++] Added RadixTreeTest to check longestMatch() does not return wrong node

* make sure longestMatch() does not return wrong node in case
  there is an existing entry where just the first character of its
  key is identical to the searchkey but the rest of the key is no
  prefix.

Change-Id: I12065d7e3bfa0d7d6c2e99422d359f291fd36e4a

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