Get no resource_name when running the list_resource_types function.

[Liu Xiaolei]

If glance does not have any resource type association，we will get IndexError when getting resource_name from list_resource_types function's response body because the function response body does not have any resource_types.

This bug is associated with three cases:
1).api/image/v2/test_images_metadefs_namespace_properties.py:MetadataNamespacePropertiesTest.test_basic_meta_def_namespace_property
2).api/image/v2/test_images_metadefs_resource_types.py:MetadataResourceTypesTest.test_basic_meta_def_resource_type_association
3).api/image/v2/test_images_metadefs_namespaces.py:MetadataNamespacesTest.test_basic_metadata_definition_namespaces

You can recurrence the bug by below actions:
1).[root@controller ~]# glance md-resource-type-list
+------+
| name |
+------+
+------+
2).[root@controller v2]# nosetests -v test_images_metadefs_namespaces.py:
tempest.api.image.v2.test_images_metadefs_namespaces.MetadataNamespacesTest.test_basic_metadata_definition_namespaces[id-319b765e-7f3d-4b3d-8b37-3ca3876ee768] ... ERROR
Traceback (most recent call last):
  File "/root/tempest-pike/tempest/api/image/v2/test_images_metadefs_namespaces.py", line 31, in test_basic_metadata_definition_namespaces
    resource_name = body['resource_types'][0]['name']
IndexError: list index out of range

This error happens because the body does not have any resource_types.

We should judge whether the list_resource_types response body contains resource_types before getting the resource_name.If there is no resource_types,we shoule set one initialized resource_name to getting the test going on.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/623924

[OpenStack Infra (hudson-openstack)]

Change abandoned by Liu Xiaolei (<email address hidden>) on branch: master
Review: https://review.openstack.org/623924

[Soumya Purohit (sp545d)]

Rather than assigning a random value to resource name a skip check can be added if the deployment does not have image metadata. If the resource_types is empty and we can skip the test.

[OpenStack Infra (hudson-openstack)]

Change abandoned by Soumya Purohit (<email address hidden>) on branch: master
Review: https://review.opendev.org/672346
Reason: Abandoning as blacklisted in downstream CI

[Doug Schveninger (ds6901)]

Since having no metadata defined is a deployment choice we have decided this better to abandon Soumya PS and handle this through blacklist in the downstream CI

[Doug Schveninger (ds6901)]

We can close this bug