generic: Add copy test that overwrites data

Using copy to overwrite data in the destination file is perfectly
valid, so let's make sure this case works as expected.

Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Eryu Guan <eguan@redhat.com>
3 files changed