test_service: Fix ++ race by using atomics.
test_service: Fix ++ race by using atomics.

Change-Id: I926dcd41134eb7c53e5d848b05bcd48d94bc1c4a
Reviewed-on: http://gerrit.aldebaran.lan/28303
Reviewed-by: mnottale <e3ccf1b6558404e921a21fa09cebb1153b50ec36@aldebaran-robotics.com>
Tested-by: mnottale <e3ccf1b6558404e921a21fa09cebb1153b50ec36@aldebaran-robotics.com>

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