Fix 'connector' parameter in update attachments API

The 'connector' parameter in update attachments is not optional
in API implementation. This patch is to set the 'connector' to
be manadatory.

Change-Id: Id58abaa9ee345b274ebfbe6b89c1047f2e580ff3

api-ref/source/v3/attachments.inc

@@ -224,7 +224,7 @@ Request
 
    - project_id: project_id_path
    - attachment_id: attachment_id_1
-   - connector: connector
+   - connector: connector_1
 
 Request Example
 ---------------

api-ref/source/v3/parameters.yaml

@@ -548,6 +548,14 @@ connector:
   in: body
   required: false
   type: object
+connector_1:
+  description: |
+    The ``connector`` object. The internal structure of connector depends on
+    the volume driver implementation. For details about the required elements
+    in the structure, see the documentation for the volume driver.
+  in: body
+  required: true
+  type: object
 consistencygroup_id:
   description: |
     The UUID of the consistency group.