Research a way to start gazebo server on remote machine

[KaiL4eK]

• Research way to work remotely
• Check how to reset world with models without gazebo server reset

[KaiL4eK]

• Start gazebo remotely / nodes locally (spawn from local machine)
• Create/Delete robot with full removal (with TF cleaning if required)
• Namespaces for each robot
• Remote connection to gzserver from local gzclient

[PonomarevDA]

I found the way to separately start gz_server and spawn/delete model of a robot. I have 2 very usual files to start gazebo server and to spawn a robot model and start slam/localization. You may not look at them if it's not required. More interest in removing of a robot model - look at this very short file. To delete a robot model I use ~/delete_model gazebo service. So, at first view it's work good. In this moment there are 2 issues:

1. We want to remove an old model and create new in a single launch file. But we should wait for a little time after removing model before spawning, otherewise robot will spawn in old position and it will have some problems (I think that with TF). There is a way to set delay between starting nodes. I'm going to try it few later.
2. I have not tested namespaces for each robot yet.

[PonomarevDA]

I've tested launching files with a delay using timed_roslaunch package. Model deletion and spawning works very well now with a delay of only 0.1 sec. Here is the example of launch file with delays. So, the last problem is Namespaces for each robot.