failure in a child agent launch should probably abort the whole launch?
fix use of _pa_clients so it is consistently indexed by resource ID of the (sub)platforms (not by the instrument_id that are keys in _pnode.subplatforms). This will fix potential misbehavior when a sub-platform is terminated externally and the parent platform would not detect that termination.
add test_with_leaf_subplatform_directly_stopped
note about _ia_clients (as contrasted with _pa_clients)
add test_with_intermediate_subplatform_directly_stopped

(note comment about leaked processes corresponding to the orphaned sub-platforms)
Merge pull request #2208 from carueda/platform_agent_robustness2

Platform agent robustness2