Requeue all soft deleted namespaces and projects

The first take on this problem involved a worker requeueing 256 of these
per 4 hours. Than it was suggested that this might not be needed, and
post deployment migrations could be used.

Given we monitor the number of projects which are pending deletion, we
could give this strategy a try and take a look about a few hours later
to see how this fares.

db/post_migrate/20161107200810_requeue_pending_delete.rb

+class RequeuePendingDelete < ActiveRecord::Migration
+  include Gitlab::Database::MigrationHelpers
+
+  DOWNTIME = false
+
+  # When using the methods "add_concurrent_index" or "add_column_with_default"
+  # you must disable the use of transactions as these methods can not run in an
+  # existing transaction. When using "add_concurrent_index" make sure that this
+  # method is the _only_ method called in the migration, any other changes
+  # should go in a separate migration. This ensures that upon failure _only_ the
+  # index creation fails and can be retried or reverted easily.
+  #
+  # To disable transactions uncomment the following line and remove these
+  # comments:
+  # disable_ddl_transaction!
+
+  def up
+    admin = User.find_by(admin: true)
+
+    Group.with_deleted.where.not(deleted_at: nil).find_each do |group|
+      GroupDestroyWorker.perform_async(group.id, admin.id)
+    end
+
+    Project.unscoped.where(pending_delete: true).find_each do |project|
+      ProjectDestroyWorker.perform_async(project.id, admin.id)
+    end
+  end
+
+  def down
+    # Noop
+  end
+end