test_timestamp09 fails with timestamp sizes other than 8 due to leading zeros in the error message:
AssertionError: in error output, expected pattern "oldest timestamp 3 must not be later than stable timestamp 1", but got "[1515669928:80699][1065:0x7f9ba2105740], test_timestamp09.test_timestamp09.test_timestamp_api, WT_CONNECTION.set_timestamp: set_timestamp: oldest timestamp 03 must not be later than stable timestamp 01: Invalid argument
cf http://build.wiredtiger.com:8080/job/wiredtiger-test-timestamp-size/144/console