Be able to assert on each specific node output

[mathieucarbou]

Currently we are doing assertions on the log output of the nodes, but when having multiple node this is made harder since system out contains a mix of all these logs. So this is hard (or not possible) to determine easily which logs are for which process.

It would be nice to be able, like the ConfigToolExecutionResult, to have access to a buffer of log lines per node, to avoid mistakes and ensure the assertions are correctly done on the right data.

[mathieucarbou]

Note: I have sent a PR in our project with a workaround to show what we need.