Compare pointers for std::ostream

operator== for std::ostream is not defined by standard

Change-Id: I403195cb955056333c823bdcd713c5e7b9be784f
Reviewed-on: http://gerrit.aldebaran.lan/51412
Reviewed-by: ncornu <ncornu@aldebaran-robotics.com>
Tested-by: ncornu <ncornu@aldebaran-robotics.com>