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>

PathPlanning/Eta3SplineTrajectory/eta3_spline_trajectory.py

@@ -17,7 +17,8 @@ import matplotlib.pyplot as plt
 from matplotlib.collections import LineCollection
 import sys
 import os
-sys.path.append(os.path.relpath("../Eta3SplinePath"))
+sys.path.append(os.path.dirname(os.path.abspath(__file__)) +
+                "/../Eta3SplinePath")
 
 try:
     from eta3_spline_path import Eta3Path, Eta3PathSegment