Suppress warning about missing `.gitlab-ci.yml` if builds are disabled

When user disables GitLab Ci Service in project's settings then warning
about missing `.gitlab-ci.yml` file should be supressed. This a matter
of user experience as stated in #3761 (closes #3761).

spec/features/commits_spec.rb

@@ -60,6 +60,7 @@ describe "Commits" do
     end
 
     describe ".gitlab-ci.yml not found warning" do
+      context 'ci service enabled' do
         it "does not show warning" do
           visit ci_status_path(@commit)
           expect(page).not_to have_content ".gitlab-ci.yml not found in this commit"
@@ -71,5 +72,18 @@ describe "Commits" do
           expect(page).to have_content ".gitlab-ci.yml not found in this commit"
         end
       end
+
+      context 'ci service disabled' do
+        before do
+          allow_any_instance_of(GitlabCiService).to receive(:active).and_return(false)
+          stub_ci_commit_yaml_file(nil)
+          visit ci_status_path(@commit)
+        end
+
+        it 'does not show warning' do
+          expect(page).not_to have_content '.gitlab-ci.yml not found in this commit'
+        end
+      end
+    end
   end
 end