pysession: bind isConnected()

Change-Id: Ifbaea9c6341688bdd13daa261563934ffbb03f09
Reviewed-on: http://gerrit.aldebaran.lan/43060
Reviewed-by: dmerejkowsky <dmerejkowsky@aldebaran-robotics.com>
Reviewed-by: pdaouadi <pdaouadi@aldebaran-robotics.com>
Tested-by: pdaouadi <pdaouadi@aldebaran-robotics.com>