Fix namespacing for multiple instances of gazebo_ros2_control plugin (backport #181)

[mergify]

Fixes the issue described in #127
It appears that when adding __ns tags to ros args on nodes that have already been namespaced, something odd happens.
I'm not too sure what happens on the rclcpp node side of things but removing the additional namespace tags on the args seems to fix the issue for me at least.
I'm running Humble on 22.04 so I've only tested against the humble branch.
I also removed the additional RCL_ROS_ARGS_FLAG in the arguments because I don't think it was doing anything.
Cheers Ben

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This is an automatic backport of pull request #181 done by Mergify.

[IslamTagi]

How soon can this be merged in as I am currently having namespacing problems when I run 2 instances of a position_controller.
my /agent_0/controller_manager and /agent_1/controller_manager are correctly configured and I can start 2 instances of the joint_state_broadcaster but when trying to do the same for the position_controller, the latter one is always set to "unconfigured". Does this PR solve this? If so, how soon will it be merged, or is there a way I can use the same changes on my local workspace?

For reference, this is my current setup
I am running Humble on WSL 22.04

I should also say the namespacing works fine when it is one robot, but when I add a second agent it stops working

[christophfroehlich]

you always can compile the branch of this PR from source. even if it is merged now, it will take a couple of weeks to be released as a binary

[IslamTagi]

@christophfroehlich do you mind running me through how i can compile this so that my workspace uses this customized version of the package? When I cloned and tried building it I ran into errors and I am fairly new to this so am not sure if I am making a mistake

[christophfroehlich]

Checkout the mergify/bp/humble/pr-181 branch of this repository in your workspace and compile it with colcon. maybe you have to uninstall the installed binary (sudo apt-get remove ros-humbe-gazebo-ros2-control)

[IslamTagi]

Checkout the mergify/bp/humble/pr-181 branch of this repository in your workspace and compile it with colcon. maybe you have to uninstall the installed binary (sudo apt-get remove ros-humbe-gazebo-ros2-control)

Worked a charm, thank you for your support!