Fix ModuleNotFoundError when executing test in the tests folder and little improve MPC controller (#619)

* Fix ModuleNotFoundError when executing test in the tests folder

Signed-off-by: Trung Kien <letrungkien.k53.hut@gmail.com>

* Improve model_predictive_speed_and_steer_control

- Fix typo
- Using @ for matrix multiplication instead of * with have been deprecated in CVXPY1.1
- Fix missing conftest module in test file

Signed-off-by: Trung Kien <letrungkien.k53.hut@gmail.com>

PathTracking/lqr_steer_control/lqr_steer_control.py

@@ -10,7 +10,10 @@ import matplotlib.pyplot as plt
 import math
 import numpy as np
 import sys
-sys.path.append("../../PathPlanning/CubicSpline/")
+import os
+
+sys.path.append(os.path.dirname(os.path.abspath(__file__)) +
+                "/../../PathPlanning/CubicSpline/")
 
 try:
     import cubic_spline_planner