Remove the tenant and user created for tempest

Remove the tenant and user created for tempest

According to the module [1] in tempest to parse tempest.conf,
the three params in session idenity are invalid:

[identity]
tenant_name = tempest
username = tempest
password = Tempest123!

Then there is no need to create tenant and user before running
tempest and refstack_defcore.

[1]: https://github.com/openstack/tempest/blob/14.0.0/tempest/config.py#L120

JIRA: FUNCTEST-864

Change-Id: Idac46e1e620324c584c8021c0bdf843f8823155a
Signed-off-by: Linda Wang <wangwulin@huawei.com>