Merge branch 'rc-fixup-mattermost-test-runner' into 'master'

Fix test selection in Test::Integration::Mattermost

See merge request gitlab-org/gitlab-ce!15278

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

@@ -7,11 +7,11 @@ module QA
         # including staging and on-premises installation.
         #
         class Mattermost < Scenario::Entrypoint
-          tags :mattermost
+          tags :core, :mattermost
 
           def perform(address, mattermost, *files)
             Runtime::Scenario.mattermost = mattermost
-            super(address, files)
+            super(address, *files)
           end
         end
       end