[api-ref] Add snapshot metadata key api

The patch did:
1. Add the missing GET/DELETE/PUT api-ref for snapshot metadata key.
2. Fix snapshot_id description.

Change-Id: I817b1ccffd5e929bcf78b913d666073596b93612

api-ref/source/v3/parameters.yaml

@@ -132,11 +132,11 @@ resource:
   in: path
   required: false
   type: string
-snapshot_id_1:
+snapshot_id_path:
   description: |
     The UUID of the snapshot.
   in: path
-  required: false
+  required: true
   type: string
 transfer_id:
   description: |
@@ -1135,6 +1135,12 @@ meta:
   in: body
   required: true
   type: object
+meta_1:
+  description: |
+    The metadata key and value pair for the snapshot.
+  in: body
+  required: true
+  type: object
 metadata:
   description: |
     One or more metadata key and value pairs for the

api-ref/source/v3/samples/snapshot-metadata-show-key-response.json

@@ -0,0 +1,5 @@
+{
+  "meta": {
+    "name": "test"
+  }
+}

api-ref/source/v3/samples/snapshot-metadata-update-key-request.json

@@ -0,0 +1,5 @@
+{
+  "meta": {
+    "name": "new_name"
+  }
+}

api-ref/source/v3/samples/snapshot-metadata-update-key-response.json

@@ -0,0 +1,5 @@
+{
+  "meta": {
+    "name": "new_name"
+  }
+}

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

@@ -186,7 +186,7 @@ Request
 .. rest_parameters:: parameters.yaml
 
    - project_id: project_id_path
-   - snapshot_id: snapshot_id
+   - snapshot_id: snapshot_id_path
 
 
 Response Parameters
@@ -235,7 +235,7 @@ Request
 
    - metadata: metadata
    - project_id: project_id_path
-   - snapshot_id: snapshot_id
+   - snapshot_id: snapshot_id_path
 
 Request Example
 ---------------
@@ -269,7 +269,7 @@ Request
 
    - metadata: metadata
    - project_id: project_id_path
-   - snapshot_id: snapshot_id
+   - snapshot_id: snapshot_id_path
 
 Request Example
 ---------------
@@ -303,7 +303,7 @@ Request
 .. rest_parameters:: parameters.yaml
 
    - project_id: project_id_path
-   - snapshot_id: snapshot_id
+   - snapshot_id: snapshot_id_path
 
 
 Response Parameters
@@ -351,7 +351,7 @@ Request
    - description: description
    - name: name
    - project_id: project_id_path
-   - snapshot_id: snapshot_id
+   - snapshot_id: snapshot_id_path
 
 Request Example
 ---------------
@@ -399,4 +399,103 @@ Request
 .. rest_parameters:: parameters.yaml
 
    - project_id: project_id_path
-   - snapshot_id: snapshot_id
+   - snapshot_id: snapshot_id_path
+
+
+
+
+Show a snapshot's metadata for a specific key
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+.. rest_method::  GET /v3/{project_id}/snapshot/{snapshot_id}/metadata/{key}
+
+Shows metadata for a snapshot for a specific key.
+
+Normal response codes: 200
+
+
+Request
+-------
+
+.. rest_parameters:: parameters.yaml
+
+   - project_id: project_id_path
+   - snapshot_id: snapshot_id_path
+   - key: key_2
+
+
+Response Parameters
+-------------------
+
+.. rest_parameters:: parameters.yaml
+
+   - meta: meta_1
+
+
+
+Response Example
+----------------
+
+.. literalinclude:: ./samples/snapshot-metadata-show-key-response.json
+   :language: javascript
+
+
+
+Delete a snapshot's metadata
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+.. rest_method::  DELETE /v3/{project_id}/snapshots/{snapshot_id}/metadata/{key}
+
+Deletes metadata for a snapshot.
+
+Normal response codes: 200
+
+
+Request
+-------
+
+.. rest_parameters:: parameters.yaml
+
+   - project_id: project_id_path
+   - snapshot_id: snapshot_id_path
+   - key: key_1
+
+
+Update a snapshot's metadata for a specific key
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+.. rest_method::  PUT /v3/{project_id}/snapshots/{snapshot_id}/metadata/{key}
+
+Update metadata for a snapshot for a specific key.
+
+Normal response codes: 200
+
+
+Request
+-------
+
+.. rest_parameters:: parameters.yaml
+
+   - project_id: project_id_path
+   - snapshot_id: snapshot_id_path
+   - key: key_3
+   - meta: meta_1
+
+Request Example
+---------------
+
+.. literalinclude:: ./samples/snapshot-metadata-update-key-request.json
+   :language: javascript
+
+Response Parameters
+-------------------
+
+.. rest_parameters:: parameters.yaml
+
+   - meta: meta_1
+
+Response Example
+----------------
+
+.. literalinclude:: ./samples/snapshot-metadata-update-key-response.json
+   :language: javascript