'Open the parent-flow logs collection for writing or create a new one.
If we receive a logs_collection_urn here it is being passed from the parent
flow runner into the new runner created by the flow object.
For a regular flow the call sequence is:
flow_runner --StartFlow--> flow object --CreateRunner--> (new) flow_runner
For a hunt the call sequence is:
hunt_runner --CallFlow--> flow_runner --StartFlow--> flow object
--CreateRunner--> (new) flow_runner
Args:
logs_collection_urn: RDFURN pointing to parent logs collection
Returns:
The LogCollection.
Raises:
RuntimeError: on parent missing logs_collection.'

def OpenLogCollection(self, logs_collection_urn):

    return grr_collections.LogCollection(self._GetLogCollectionURN(logs_collection_urn), token=self.token)
