Merge branch 'make-mirror-settings-exclusive-to-gitlab-com' into 'master'

Make mirror specific admin application settings exclusive to Gitlab.com

See merge request !2307

app/views/admin/application_settings/_repository_mirrors_form.html.haml

-%fieldset
+- if Gitlab.com?
+  %fieldset
     %legend Repository mirror settings
     .form-group
       = f.label :mirror_max_delay, class: 'control-label col-sm-2' do

changelogs/unreleased-ee/make-mirror-settings-exclusive-to-gitlab-com.yml

+---
+title: Make admin mirror application setting Gitlab.com exclusive
+merge_request: 2307
+author: