In Python tests w/ tiered storage, we'll configure bucket directory to be ./bucket (and the current home directory happens to be the database directory).  After running, we want to look at the contents of the directory, and we do:

$ cd build_posix
$ ./wt -h WT_TEST/test_tiered* list 

  But we get an error that it can't open ./bucket - it can't because it's trying to open build_posix/bucket.  The workaround of course is to run the wt command in the same directory as the original test ran.  Sensible, but inconvenient.  Better to interpret a relative directory used for bucket (or cache) dir as relative to the database home direcotry.