Given two node names that identify a link, return the pair of
        interface names assigned at each endpoint (as a tuple in the 
        same order as the nodes given).

def getLinkInterfaces(self, node1, node2):
        '''
        Given two node names that identify a link, return the pair of
        interface names assigned at each endpoint (as a tuple in the 
        same order as the nodes given).
        '''
        linkdata = self.getLink(node1,node2)
        return linkdata[node1],linkdata[node1]