un-skip test of launching network of 13 platforms and 8 instruments

 (locally this test ran in 329.336s)
add test_instrument_reset_externally
add test_adverse_activation_sequence
indicate expected_state=ResourceAgentState.STREAMING in _instruments_start_streaming
some refactor to facilitate further test cases
add test_with_instrument_directly_put_into_streaming
add test_with_instrument_directly_stopped
minor cleanup: remove duplicate import; reformat a log msg
cleanup: remove unreachable conditioned code and align some logging to common pattern in platform agent
remove obsolete TODO comment
fix typo in condition under logging.TRACE
adjust a few log statements for consistency (use platform_id as prefix as general pattern)
adjust log statements for consistency (use platform_id as prefix as general pattern)
fix missing argument in call to _remove_exclusive_access in rollback section
explicitly verify expected mission events including validation of execution_status field value
Merge pull request #2199 from carueda/platform_agent_robustness

additional platform agent tests to check robustness
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)