Fix "Creates an aggregate" parameters

"Creates an aggregate" API supports multiple parameters on a request,
but api-ref doesn.t contain them at all This patch adds them.

The following JSON-Schema is for the API.
https://github.com/openstack/nova/blob/master/nova/api/openstack/compute/schemas/aggregates.py#L32

Part of bp:api-ref-in-rst

Change-Id: I3a58568662d21059bccdcf64cc30dbf3b706db58

api-ref/source/parameters.yaml

@@ -34,6 +34,12 @@ aggregate_id:
   in: path
   required: true
   type: string
+aggregate_name:
+  description: |
+    The name of the aggregate.
+  in: body
+  required: true
+  type: string
 alias_1:
   description: |
     An alias for the extension name. For example, ``os-server-external-events``.