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
diff --git a/ironic_tempest_plugin/config.py b/ironic_tempest_plugin/config.py
index 819051e..79b6d18 100644
--- a/ironic_tempest_plugin/config.py
+++ b/ironic_tempest_plugin/config.py
@@ -199,6 +199,5 @@
                help="The driver to set on the newly discovered nodes. "
                     "Only has effect with auto_discovery_feature is True."),
     cfg.StrOpt('data_store',
-               default='swift',
                help="The storage backend for storing introspection data."),
 ]
diff --git a/ironic_tempest_plugin/tests/scenario/test_introspection_basic.py b/ironic_tempest_plugin/tests/scenario/test_introspection_basic.py
index 6df1207..9823a88 100644
--- a/ironic_tempest_plugin/tests/scenario/test_introspection_basic.py
+++ b/ironic_tempest_plugin/tests/scenario/test_introspection_basic.py
@@ -94,7 +94,12 @@
         for node_id in self.node_ids:
             node = self.node_show(node_id)
             self.assertEqual('yes', node['extra']['rule_success'])
-            if CONF.baremetal_introspection.data_store != "none":
+            data_store = CONF.baremetal_introspection.data_store
+            if data_store is None:
+                # Backward compatibility, the option is not set.
+                data_store = ('swift' if CONF.service_available.swift
+                              else 'none')
+            if data_store != 'none':
                 self.verify_node_introspection_data(node)
             self.verify_node_flavor(node)
 
diff --git a/ironic_tempest_plugin/tests/scenario/test_introspection_discovery.py b/ironic_tempest_plugin/tests/scenario/test_introspection_discovery.py
index 846fcfd..6f92d43 100644
--- a/ironic_tempest_plugin/tests/scenario/test_introspection_discovery.py
+++ b/ironic_tempest_plugin/tests/scenario/test_introspection_discovery.py
@@ -156,7 +156,12 @@
 
         inspected_node = self.node_show(self.node_info['name'])
         self.verify_node_flavor(inspected_node)
-        if CONF.baremetal_introspection.data_store != "none":
+        data_store = CONF.baremetal_introspection.data_store
+        if data_store is None:
+            # Backward compatibility, the option is not set.
+            data_store = ('swift' if CONF.service_available.swift
+                          else 'none')
+        if data_store != 'none':
             self.verify_node_introspection_data(inspected_node)
         self.assertEqual(ProvisionStates.ENROLL,
                          inspected_node['provision_state'])