Fix unit tests to properly marked deleted files

The unit tests were playing fast and loose with the tombstone marker,
where the test framework was setting up a DiskFile object which had
its data written to the .ts file, not the .data file. This behavior
did not reflect how the interfaces to DiskFile were supposed to
work.

Change-Id: Idd6e8882e062ba2e13489f14189223ab4158677c
Signed-off-by: Peter Portante <peter.portante@redhat.com>