Adding ability to use Diagnostics Updater and self test in nodelets

Right now the Updater and self test create node handles internally and provide no way to supply node handles instead. This prevents nodelets from properly using these diagnostics tools if multiple nodelets try to use them. For example if multiple nodelets try to use self test they will both end up trying to advertise the self test service using the private node handle for the nodelet manager instead of under the name of the node.