iotests: Fix cleanup path in some tests

Some iotests leave behind some external data file when run for qcow2
with -o data_file.  Fix that.

Signed-off-by: Max Reitz <mreitz@redhat.com>
Message-Id: <20200224171631.384314-1-mreitz@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Max Reitz <mreitz@redhat.com>
3 files changed