snapshot_disk: Add snapshot_delete cases without '--metadata' option

External disk only snapshot is not supported with delete yet, but internal
snapshot delete is supported. Update test case and cfg to support testing
this.

Add filter 'delete_test' to cover 6 new delete cases, put exist cases
under 'no_delete'.

The original cases total is 27, now with 6 new delete cases, total will
be 33.

Fixed few lines with column length exceeds 80.

Signed-off-by: Wayne Sun <gsun@redhat.com>