Fix selecting the right controller given fake_hw

This was falsely introduced earlier. This is a working version.

Author: fmauch

ur_moveit_config/launch/ur_moveit.launch.py

@@ -164,7 +164,8 @@ def launch_setup(context, *args, **kwargs):
     # Trajectory Execution Configuration
     controllers_yaml = load_yaml("ur_moveit_config", "config/controllers.yaml")
     # the scaled_joint_trajectory_controller does not work on fake hardware
-    if use_fake_hardware:
+    change_controllers = context.perform_substitution(use_fake_hardware)
+    if change_controllers == "true":
         controllers_yaml["scaled_joint_trajectory_controller"]["default"] = False
         controllers_yaml["joint_trajectory_controller"]["default"] = True