Fix promise set multiple times in eventloop

Change-Id: I26108a8420021d439489c72f6a8efa0069cd12e6
Reviewed-on: http://gerrit.aldebaran.lan/50213
Reviewed-by: tfontenay <tfontenay@aldebaran-robotics.com>
Tested-by: gerrit
Reviewed-by: pdaouadi <pdaouadi@aldebaran-robotics.com>