Merge branch 'zj-fixture-fork' into 'master'

Fixture for forks

See merge request gitlab-org/gitlab-ce!23613

db/fixtures/development/24_forks.rb

+require './spec/support/sidekiq'
+
+Sidekiq::Testing.inline! do
+  Gitlab::Seeder.quiet do
+    User.all.sample(10).each do |user|
+      source_project = Project.public_only.sample
+      fork_project = Projects::ForkService.new(source_project, user, namespace: user.namespace).execute
+
+      if fork_project.valid?
+        puts '.'
+      else
+        puts 'F'
+      end
+    end
+  end
+end