Fix problems in service api doc

This patch fixes the following problems found in the api doc:

- The 'service_id' field should not appear in a service create request;
- The 'enabled', 'description' fields should be optional when doing a
  service update.

Change-Id: Iac91a9f2d29a458f1e3eb93e64fea6a508b9980c

api-ref/source/v3/parameters.yaml

@@ -1537,6 +1537,12 @@ service_description:
   in: body
   required: true
   type: string
+service_description_notRequired:
+  description: |
+    The service description.
+  in: body
+  required: false
+  type: string
 service_enabled:
   description: |
     Defines whether the service and its endpoints
@@ -1573,7 +1579,7 @@ service_name:
   description: |
     The service name.
   in: body
-  required: false
+  required: true
   type: string
 service_type:
   description: |

api-ref/source/v3/service-catalog.inc

@@ -80,7 +80,6 @@ Request
    - description: service_description
    - service: service
    - enabled: service_enabled
-   - service_id: service_id
    - type: service_type
    - name: service_name
 
@@ -367,8 +366,8 @@ Request
 .. rest_parameters:: parameters.yaml
 
    - type: service_type
-   - enabled: service_enabled
-   - description: service_description
+   - enabled: service_enabled_notRequired
+   - description: service_description_notRequired
    - service: service
    - name: service_name
    - service_id: service_id_path