Add tests for mattermost login via oauth

* Adds Runtime::Scenario as a place to record the properties of the
  Scenario we're interested in.

* Adds a positional argument to Test::Integration::Mattermost to specify
  Runtime::Scenario.mattermost

* Adds Page::Mattermost::{Main,Login} to model the mattermost pages we
  need to interact with.

* Adds qa/features/mattermost/login_spec to perform a login via oauth
  and ensure we are logged in.

qa/qa.rb

@@ -8,6 +8,7 @@ module QA
     autoload :Release, 'qa/runtime/release'
     autoload :User, 'qa/runtime/user'
     autoload :Namespace, 'qa/runtime/namespace'
+    autoload :Scenario, 'qa/runtime/scenario'
   end
 
   ##
@@ -80,6 +81,11 @@ module QA
     module Admin
       autoload :Menu, 'qa/page/admin/menu'
     end
+
+    module Mattermost
+      autoload :Main, 'qa/page/mattermost/main'
+      autoload :Login, 'qa/page/mattermost/login'
+    end
   end
 
   ##

qa/qa/page/mattermost/login.rb

+module QA
+  module Page
+    module Mattermost
+      class Login < Page::Base
+        def initialize
+          visit(Runtime::Scenario.mattermost + '/login')
+        end
+
+        def sign_in_using_oauth
+          click_link class: 'btn btn-custom-login gitlab'
+
+          if page.has_content?('Authorize GitLab Mattermost to use your account?')
+            click_button 'Authorize'
+          end
+        end
+      end
+    end
+  end
+end

qa/qa/page/mattermost/main.rb

+module QA
+  module Page
+    module Mattermost
+      class Main < Page::Base
+        def initialize
+          visit(Runtime::Scenario.mattermost)
+        end
+      end
+    end
+  end
+end

qa/qa/runtime/scenario.rb

+module QA
+  module Runtime
+    module Scenario
+      extend self
+      attr_accessor :mattermost
+    end
+  end
+end

qa/qa/scenario/test/integration/mattermost.rb

@@ -8,6 +8,11 @@ module QA
         #
         class Mattermost < Scenario::Entrypoint
           tags :core, :mattermost
+
+          def perform(address, mattermost, *files)
+            Runtime::Scenario.mattermost = mattermost
+            super(address, files)
+          end
         end
       end
     end

qa/qa/specs/features/mattermost/login_spec.rb

+module QA
+  feature 'logging in to Mattermost', :mattermost do
+    scenario 'can use gitlab oauth' do
+      Page::Main::Entry.act { sign_in_using_credentials }
+      Page::Mattermost::Login.act { sign_in_using_oauth }
+
+      Page::Mattermost::Main.perform do |page|
+        expect(page).to have_content(/(Welcome to: Mattermost|Logout GitLab Mattermost)/)
+      end
+    end
+  end
+end