update description for Change Node Power State

This updates the description of the
'PUT /v1/nodes/{node_ident}/states/power' request to mention that
Bare Metal API version 1.27 was when:
- the 'timeout' parameter was added
- the 'soft power off' and 'soft rebooting' values were made available
  for the 'target' parameter

Change-Id: I1c720a2dd15eab1246ad672b9d7f2b8708ceec0b

api-ref/source/baremetal-api-v1-node-management.inc

@@ -302,6 +302,13 @@ Request a change to the Node's power state.
 
 Normal response code: 202 (Accepted)
 
+.. versionadded:: 1.27
+   In the request, the ``target`` value can also be one of ``soft power off``
+   or ``soft rebooting``.
+
+.. versionadded:: 1.27
+   In the request, a ``timeout`` can be specified.
+
 Error codes:
     - 409 (NodeLocked, ClientError)
     - 400 (Invalid, InvalidStateRequested, InvalidParameterValue)

api-ref/source/parameters.yaml

@@ -873,7 +873,7 @@ power_state:
   type: string
 power_timeout:
   description: |
-    Timeout for a power state transition.
+    Timeout (in seconds) for a power state transition.
   in: body
   required: false
   type: integer