Serialize stdout and stderr from test run

Some continuous integration servers like TeamCity expect log output to be in a specific format. They have rather complicated formatters for both rspec and capybara. When running with parallel_tests the processes run over one another. It would be nice if somehow each process wrote stdout and stderr to a separate file and then once the process terminated it automatically dumped the contents of that file to stdout/stderr on the original rake call. I'm not sure if this is clear or not, but basically it would provide a way to serialize log output from any formatter.