Fix tapi get-topology-details functional test

- Replace databroker with networkTransactionService in
  R2RTapiLinkDiscovery
- Add specific LOG message to enable tapi tests to
  know when the device has been successfully connected
  and translated in the TAPI topology
- Add connect_xpdr_to_rdm_tapi_request and mount_tapi_device
  tests in test_utils which will be called from
  test12_tapi_full_multi_layer

JIRA: TRNSPRTPCE-553
Signed-off-by: errea <errea@eurecom.fr>
Change-Id: Iff6811d19861521733de1667c49ba4793fa35b2c