Add description for Image location in snapshot

snapshot action nova will return image URL in response header
better to provide this info to end user for their reference.

Also, the backup header description is changed as well.

Change-Id: I15cf228b4a5a2d0dbae5fa76ec6821487e7808ed
Closes-Bug: 1657998

api-ref/source/parameters.yaml

@@ -1,4 +1,11 @@
 # variables in header
+image_location:
+  description: |
+    The image location URL of the image or backup created, HTTP header
+    "Location: <image location URL>" will be returned.
+  in: header
+  required: true
+  type: string
 tag_location:
   description: |
     The location of the tag. It's individual tag URL which can be used for

api-ref/source/servers-actions.inc

@@ -271,7 +271,9 @@ Request
 Response
 --------
 
-If successful, this method does not return content in the response body.
+.. rest_parameters:: parameters.yaml
+
+  - image_location: image_location
 
 
 Lock Server (lock Action)

api-ref/source/servers-admin-action.inc

@@ -55,8 +55,9 @@ Request
 Response
 --------
 
-If successful, the header 'Location' : <image location URL>
-will be returned. No response body is returned.
+.. rest_parameters:: parameters.yaml
+
+  - image_location: image_location
 
 
 Inject Network Information (injectNetworkInfo Action)