Fixes external_url link

Adds tests for:
  - external_url link in environmnets list
  - must show deployment internal id in environments list
  - must show build name and id in environments list

app/views/projects/deployments/_actions.haml

 - if can?(current_user, :create_deployment, deployment) && deployment.deployable
   .pull-right
   
-    - external_url = deployment.deployable.try(:external_url)
+    - external_url = deployment.environment.try(:external_url)
     - if external_url
       = link_to external_url, target: '_blank', class: 'btn external-url' do
         = icon('external-link')

spec/features/environments_spec.rb

@@ -44,6 +44,10 @@ feature 'Environments', feature: true do
         scenario 'does show deployment SHA' do
           expect(page).to have_link(deployment.short_sha)
         end
+        
+        scenario 'does show deployment internal id' do
+          expect(page).to have_content(deployment.iid)
+        end
 
         context 'with build and manual actions' do
           given(:pipeline) { create(:ci_pipeline, project: project) }
@@ -61,6 +65,20 @@ feature 'Environments', feature: true do
             expect(page).to have_content(manual.name)
             expect(manual.reload).to be_pending
           end
+          
+          scenario 'does show build name and id' do
+            expect(page).to have_link("#{build.name} (##{build.id})")
+          end
+          
+          context 'with external_url' do
+            given(:environment) { create(:environment, project: project, external_url: 'https://git.gitlab.com') }
+            given(:build) { create(:ci_build, pipeline: pipeline) }
+            given(:deployment) { create(:deployment, environment: environment, deployable: build) }
+            
+            scenario 'does show an external link button' do
+              expect(page).to have_selector('.btn.external-url')
+            end
+          end
         end
       end
     end