Adding cassandra service with a separate yaml file.

Adding cassandra service with a separate yaml file.

- Left the file samples/scenarios/service_delivery_controller_opnfv.yaml unchanged.
- Added a yaml definition of Cassandra StatefulSet and its service into a separate file under tools directory
- Cassandra Service run with 1 replica
- Deleted 'data-plane-ns' and use 'default' instead for cassandra containers.
- Revoked changes for samples/scenarios/service_delivery_controller_opnfv.yaml.
- Added new line (Wutien suggested it)

JIRA: CLOVER-000

Change-Id: I2bb4249cf2523f5011d6fefc69dc469a90e20eaf
Signed-off-by: iharijono <indra.harijono@huawei.com>