Find topics/services.
Do a lookup to find topics of the type
specified. This will raise exceptions if it times out or returns
multiple values. It can apply the additional logic of whether this should
return a single unique result, or a list.
@param topic_type : topic type specification, e.g. rocon_std_msgs/MasterInfo
@type str
@param timeout : raise an exception if nothing is found before this timeout occurs.
@type rospy.rostime.Duration
@param unique : flag to select the lookup behaviour (single/multiple results)
@type bool
@return the fully resolved name of the topic (unique) or list of names (non-unique)
@type str
@raise rocon_python_comms.NotFoundException if no topic is found within the timeout