periodictask: fix race in trigger
periodictask: fix race in trigger

Change-Id: I109f3cbbebb3f333c877af50cb7f9c906533e27c
Reviewed-on: http://gerrit.aldebaran.lan/43316
Reviewed-by: pdaouadi <fc1eb3334d3fdad315bae23aa166bc70bd434067@aldebaran-robotics.com>
Tested-by: pdaouadi <fc1eb3334d3fdad315bae23aa166bc70bd434067@aldebaran-robotics.com>

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