[builder] Set a field _node_name in environment and use it accordingly

In particular, it fixes the code for multi-node scene with cameras.
[blender] Rework a bit how we deal with component for external robot

Don't create them, and set a default_action to no_op. It can cause
issues for camera like sensor, which requires specific scene. Just set
their instance to None, and deal properly with None at different places
[blender] Fix previous
[core] In abort, check that component is not None (external_robot case)

Not sure anybody has tested properly services in multi-node
configuration
[builder] allow external node as viewers
[camera] handle multi-node