Get the identified feature

This is a simple code for connect your QgsMapToolIdentifyFeature signal.

from qgis.gui import QgsMapToolIdentifyFeature

def onFeatureIdentified(feature):
    print "feature selected : "+ str(feature.id())

mapTool = None
mc=iface.mapCanvas()
lyr=iface.activeLayer()
mapTool = QgsMapToolIdentifyFeature(mc)
mapTool.setLayer(lyr)
mc.setMapTool(mapTool)
mapTool.featureIdentified.connect(onFeatureIdentified)

And when click in a feature print the id.

Regards

Tested with QGIS 2.18.14 on W10

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UPDATE: Add GIF with QGIS 2.18.13

To stick with your code :

def onFeatureIdentified(self, ff):
    print("feature selected")

def run(self):
    mCanvas = self.iface.mapCanvas()
    f = QgsMapToolIdentifyFeature(mCanvas, self.iface.activeLayer())
    mCanvas.setMapTool(f)
    f.featureIdentified.connect(self.onFeatureIdentified)