[test][prefix] Make all databases root folder point to a valid location

This will allow the docker tests to more easily setup and
cleanup its content.

While the folder is not used as these databases are generative
only, docker will create it anyway as mounting a non-exisiting
folder will trigger its creation with the daemon ownership
applied.
7 jobs for standardize_test_database_root_folder in 4 minutes and 59 seconds (queued for 8 seconds)
Status Name Job ID Coverage
  Build
passed build_linux_36 #215734
docker

00:02:15

73.0%
passed build_linux_37 #215735
docker

00:02:18

73.0%
passed build_macosx_36 #215470
macosx

00:02:20

73.0%
passed build_macosx_37 #215471
macosx

00:02:19

73.0%
failed build_linux_36 #215549
docker

failed build_linux_36 #215472
docker

failed build_linux_37 #215473
docker