Add list resource provider usage

Add a method to return the current resource usage for a specific
resource provider. Given a specific rp_uuid return the resource
providers current generation as well as its assoicated resource class
usage at that time. Example output below:

(Pdb) self.resource_providers_client.list_resource_provider_usages('90234521-0f4f-4777-98d8-731db8e61a0d')
{'resource_provider_generation': 52, 'usages': {'VGPU': 1}}

More details of the api can be referenced here [1]

[1] https://docs.openstack.org/api-ref/placement/#resource-provider-usages

Change-Id: I13ca77f1cd8fbf74cd716b2d8eae772f5328a4d4

releasenotes/notes/add-placement-usage-client-method-8b6015cbd8a5e0f6.yaml

@@ -0,0 +1,8 @@
+---
+features:
+  - |
+    Add ``placement`` API usage method for evaluating resource class
+    utilization of the resource provider. The following API call is available
+    for tempest from now in the resource_providers_client:
+
+    * GET /resource_providers/{uuid}/usages

tempest/lib/services/placement/resource_providers_client.py

@@ -26,6 +26,7 @@ class ResourceProvidersClient(base_placement_client.BasePlacementClient):
     * resource providers
     * resource provider inventories
     * resource provider aggregates
+    * resource provider usages
     """
 
     def list_resource_providers(self, **params):
@@ -69,6 +70,19 @@ class ResourceProvidersClient(base_placement_client.BasePlacementClient):
         body = json.loads(body)
         return rest_client.ResponseBody(resp, body)
 
+    def list_resource_provider_usages(self, rp_uuid):
+        """List resource provider usages.
+
+        For full list of available parameters, please refer to the official
+        API reference:
+        https://docs.openstack.org/api-ref/placement/#list-resource-provider-usages
+        """
+        url = '/resource_providers/%s/usages' % rp_uuid
+        resp, body = self.get(url)
+        self.expected_success(200, resp.status)
+        body = json.loads(body)
+        return rest_client.ResponseBody(resp, body)
+
     def list_resource_provider_aggregates(self, rp_uuid):
         """List resource provider aggregates.
 

tempest/tests/lib/services/placement/test_resource_providers_client.py

@@ -85,6 +85,14 @@ class TestResourceProvidersClient(base.BaseServiceTest):
         },
         "resource_provider_generation": 1
     }
+    FAKE_RESOURCE_PROVIDER_USAGES = {
+        "usages": {
+            "VCPU": 2,
+            "MEMORY_MB": 1024,
+            "DISK_GB": 10
+        },
+        "resource_provider_generation": 3
+    }
 
     def setUp(self):
         super(TestResourceProvidersClient, self).setUp()
@@ -180,3 +188,19 @@ class TestResourceProvidersClient(base.BaseServiceTest):
 
     def test_list_resource_provider_aggregates_with_bytes_body(self):
         self._test_list_resource_provider_aggregates(bytes_body=True)
+
+    def _test_list_resource_provider_usages(self, bytes_body=False):
+        self.check_service_client_function(
+            self.client.list_resource_provider_usages,
+            'tempest.lib.common.rest_client.RestClient.get',
+            self.FAKE_RESOURCE_PROVIDER_USAGES,
+            to_utf=bytes_body,
+            status=200,
+            rp_uuid=self.FAKE_RESOURCE_PROVIDER_UUID
+        )
+
+    def test_show_resource_provider_usages_with_str_body(self):
+        self._test_list_resource_provider_inventories()
+
+    def test_show_resource_provider_usages_with_with_bytes_body(self):
+        self._test_list_resource_provider_inventories(bytes_body=True)