api-ref: fix addFloatingIp action docs

As described in the bug, the addFloatingIp parameter
in the request body is an object, not a string. And we
didn't actually have an example request, so one is added
here to further clarify the API.

Change-Id: I366ba880cf13558291da286e6524327cafcccf1f
Closes-Bug: #1636185

api-ref/source/parameters.yaml

@@ -806,10 +806,11 @@ addFixedIp:
   type: string
 addFloatingIp:
   description: |
-    The action.
+    The action. Contains required floating IP ``address`` and optional
+    ``fixed_address``.
   in: body
   required: true
-  type: string
+  type: object
 address:
   description: |
     The floating IP address.

api-ref/source/servers-actions.inc

@@ -67,11 +67,10 @@ Request
   - address: address
   - fixed_address: fixed_address
 
-.. TODO(gmann) Need to create the sample file for this action.
-   **Example Add (Associate) Floating Ip (addFloatingIp Action): JSON request**
+**Example Add (Associate) Floating Ip (addFloatingIp Action): JSON request**
 
-   .. literalinclude:: ../../doc/api_samples/os-floating-ips/floating-ips-create-resp.json
-      :language: javascript
+.. literalinclude:: ../../doc/api_samples/servers/server-action-addfloatingip.json
+  :language: javascript
 
 Response
 --------