Logger in Evergreen adds timestamp at the front of each log line by default, which is useful in most of the use cases. The test/format CONFIG dump is an exception, as people want to copy/paste it and use the content to run the test/format program. The timestamp in front of each CONFIG line introduces an extra tidy-up step which is undesired and should be avoided. 

See WT-5521 for a current test/format CONFIG dump example, and discussion regarding removing the timestamp info.