Compatible with old Swift service enable

Some of gate job, like ironic-inspector-tempest-dsvm-python3 doesn't
support data stores in Swift[1]. If use swift as tempest default
config, it will breaks that stable branch gate job.

This patch add backward compatibility for swift, and lets default data_store
is None.

[1] https://github.com/openstack/ironic-inspector/blob/stable/rocky/devstack/plugin.sh#L271-L273

Change-Id: Id349ab8c1cf90632032233c7a754e60544efd057
3 files changed