issue ros-simulation#408 this should fix the timestamp to the time th…

…e most recent image was acquired in the sim.

Haven't tested because getting:

    unsupported pickle protocol: 4
    log4cxx: Could not read configuration file [/home/lucasw/.ros/rosconsole.config].
    log4cxx: Could not read configuration file [/home/lucasw/.ros/rosconsole.config].
    [urdf_spawner-3] process has died [pid 30719, exit code 1, cmd /home/lucasw/catkin_ws/src/gazebo_ros_pkgs/gazebo_ros/scripts/spawn_model -urdf -model rrbot -param robot_description __name:=urdf_spawner __log:=/home/lucasw/.ros/log/f00e5c50-ec35-11e5-98b1-00dbdf11ceac/urdf_spawner-3.log].
    log file: /home/lucasw/.ros/log/f00e5c50-ec35-11e5-98b1-00dbdf11ceac/urdf_spawner-3*.log

when trying to run rrbot_gazebo.  gazebo by itself seems to launch though.

gazebo_plugins/src/gazebo_ros_camera.cpp

@@ -76,7 +76,7 @@ void GazeboRosCamera::OnNewFrame(const unsigned char *_image,
     unsigned int _width, unsigned int _height, unsigned int _depth,
     const std::string &_format)
 {
-  this->sensor_update_time_ = this->parentSensor_->GetLastUpdateTime();
+  common::Time sensor_update_time = this->parentSensor_->GetLastUpdateTime();
 
   if (!this->parentSensor->IsActive())
   {
@@ -91,8 +91,8 @@ void GazeboRosCamera::OnNewFrame(const unsigned char *_image,
       common::Time cur_time = this->world_->GetSimTime();
       if (cur_time - this->last_update_time_ >= this->update_period_)
       {
-        this->PutCameraData(_image);
-        this->PublishCameraInfo();
+        this->PutCameraData(_image, sensor_update_time);
+        this->PublishCameraInfo(sensor_update_time);
         this->last_update_time_ = cur_time;
       }
     }