Add timestamps to API pipelines responses

Adds the created_at and updated_at attributes to responses from the
API pipelines endpoints.

changelogs/unreleased/add-timestamps-to-api-pipelines-response.yml

+---
+title: Added timestamps (created_at and updated_at) to API pipelines response
+merge_request: 17911
+author:
+type: added

doc/api/pipelines.md

@@ -34,14 +34,18 @@ Example of response
     "status": "pending",
     "ref": "new-pipeline",
     "sha": "a91957a858320c0e17f3a0eca7cfacbff50ea29a",
-    "web_url": "https://example.com/foo/bar/pipelines/47"
+    "web_url": "https://example.com/foo/bar/pipelines/47",
+    "created_at": "2016-08-11T11:28:34.085Z",
+    "updated_at": "2016-08-11T11:32:35.169Z",
   },
   {
     "id": 48,
     "status": "pending",
     "ref": "new-pipeline",
     "sha": "eb94b618fb5865b26e80fdd8ae531b7a63ad851a",
-    "web_url": "https://example.com/foo/bar/pipelines/48"
+    "web_url": "https://example.com/foo/bar/pipelines/48",
+    "created_at": "2016-08-12T10:06:04.561Z",
+    "updated_at": "2016-08-12T10:09:56.223Z",
   }
 ]
 ```

lib/api/entities.rb

@@ -682,6 +682,7 @@ module API
 
     class PipelineBasic < Grape::Entity
       expose :id, :sha, :ref, :status
+      expose :created_at, :updated_at
 
       expose :web_url do |pipeline, _options|
         Gitlab::Routing.url_helpers.project_pipeline_url(pipeline.project, pipeline)

spec/requests/api/pipelines_spec.rb

@@ -29,7 +29,7 @@ describe API::Pipelines do
         expect(json_response.first['sha']).to match /\A\h{40}\z/
         expect(json_response.first['id']).to eq pipeline.id
         expect(json_response.first['web_url']).to be_present
-        expect(json_response.first.keys).to contain_exactly(*%w[id sha ref status web_url])
+        expect(json_response.first.keys).to contain_exactly(*%w[id sha ref status web_url created_at updated_at])
       end
 
       context 'when parameter is passed' do