Fix in api-ref

Add a separate var for snapshot and use in:
https://github.com/openstack/cinder/blob/master/api-ref/source/v3/volumes-v3-snapshots.inc

Change-Id: Ib6a153562aec1c73ceb7ad9d4f6c4ee104d768e2

api-ref/source/v3/parameters.yaml

@@ -1184,6 +1184,14 @@ force:
   in: body
   required: false
   type: boolean
+force_snapshot:
+  description: |
+    Indicates whether to snapshot, even if the volume
+    is attached. Default is ``false``.
+    See :ref:`valid boolean values <valid-boolean-values>`
+  in: body
+  required: false
+  type: boolean
 force_upload_vol:
   description: |
     Enables or disables upload of a volume that is

api-ref/source/v3/volumes-v3-snapshots.inc

@@ -122,7 +122,7 @@ Request
    - volume_id: volume_id
    - name: name_snap_req
    - description: description_snap
-   - force: force
+   - force: force_snapshot
    - metadata: metadata_snap
 
 Request Example