Spraying to a file plane should adhere to directory-per-part semantics

Spraying to a plane in a containerized system was ignoring the [default] dir-per-plane semantics.
It created a valid file that was readable, but the parts were not in separate directories.
However, when copying a file to another plane, such that the same logical file resides on mutiple planes meant that the meta information was no longer correctly represented the location of the copy that had ignored dir-per-part semantics.