Fix time type issue in time unittest (#453)
Fix time type issue in time unittest (#453)

Obviously it mean RCL_SYSTEM_TIME but not RCL_ROS_TIME in some test cases

Signed-off-by: jwang <fd1ee87cbf1cb14357ce9925a38414c16dc86417@intel.com>
ros2/rclcpp,ros2/rclcpp