Add more description to policies in the keypairs.py

This updates the policy doc for server extend controller in keypairs.py

Partial implement blueprint blueprint policy-docs

Change-Id: I32d2dae19fc2cfa99470edbb39dafd56de279b73

nova/policies/keypairs.py

@@ -13,8 +13,6 @@
 #    License for the specific language governing permissions and limitations
 #    under the License.
 
-from oslo_policy import policy
-
 from nova.policies import base
 
 
@@ -63,9 +61,20 @@ keypairs_policies = [
                 'method': 'GET'
             }
         ]),
-    policy.RuleDefault(
-        name=BASE_POLICY_NAME,
-        check_str=base.RULE_ADMIN_OR_OWNER),
+    base.create_rule_default(
+        BASE_POLICY_NAME,
+        base.RULE_ADMIN_OR_OWNER,
+        "Return 'key_name' in the response of server.",
+        [
+            {
+                'path': '/servers/{id}',
+                'method': 'GET',
+            },
+            {
+                'path': '/servers/detail',
+                'method': 'GET'
+            }
+        ]),
 ]