Python: make type conversion error more explicit
Python: make type conversion error more explicit

Change-Id: Ib25b8450c1a8083df6bdae2ff1d06803738552ce
Reviewed-on: http://gerrit.aldebaran.lan/32459
Reviewed-by: mnottale <e3ccf1b6558404e921a21fa09cebb1153b50ec36@aldebaran-robotics.com>
Reviewed-by: pdaouadi <fc1eb3334d3fdad315bae23aa166bc70bd434067@aldebaran-robotics.com>
Tested-by: pdaouadi <fc1eb3334d3fdad315bae23aa166bc70bd434067@aldebaran-robotics.com>

bsautron/libqi,vbarbaresi/libqi,aldebaran/libqi,aldebaran/libqi,aldebaran/libqi