Dump the failing CONFIG for Evergreen test/format tasks

When Evergreen jobs running test/format fail they need to add cat RUNDIR/CONFIG to the reported output. Here's one example of a failure:
https://evergreen.mongodb.com/task/wiredtiger_ubuntu1804_format_stress_sanitizer_smoke_test_fa005b0a0347f2a4bce42feb9c4a6b95cc51beb5_20_01_28_01_58_45/0

The CONFIG needs to be available in an easy to find, textual form for easy cut-and-paste. It is not reasonable to expect someone to have to spawn a host, etc just to get the CONFIG.