When calling CreateDirectory for /wfs, we were passing a UID of 19,
because that is the UID /wfs is supposed to have. However,
CreateDirectory returns AccessDenied if we try to create a directory in
the root using a UID other than 0.
To fix this, let's use UID 0 to create the directory, and then change
the UID and GID afterwards using SetMetadata. This is what the ESCore
constructor does, which is the piece of code that normally creates /wfs.