Task metadata should be written regardless of whether a Task runs to completion.

It should also be guaranteed to be independent for each invocation of the Task's run method, or at least invocation of each parent CmdLineTask's runDataRef (or equivalent) method. This may be difficult to ensure because the metadata is currently an instance attribute of the Task and hence may be shared between method calls. It may also already be handled correctly (which would make this part of the ticket just verification of that).