Merge branch '46630-add-missing-columns-to-project-mirror-data' into 'master'

Upgrading from EE to CE fails on project_mirror_data migrations

Closes #46630

See merge request gitlab-org/gitlab-ce!19109

changelogs/unreleased/46630-add-missing-columns-to-project-mirror-data.yml

+---
+title: Fix project mirror database inconsistencies when upgrading from EE to CE
+merge_request: 19109
+author:
+type: fixed

db/migrate/20180503175053_ensure_missing_columns_to_project_mirror_data.rb

+class EnsureMissingColumnsToProjectMirrorData < ActiveRecord::Migration
+  include Gitlab::Database::MigrationHelpers
+
+  DOWNTIME = false
+
+  def up
+    add_column :project_mirror_data, :status, :string unless column_exists?(:project_mirror_data, :status)
+    add_column :project_mirror_data, :jid, :string unless column_exists?(:project_mirror_data, :jid)
+    add_column :project_mirror_data, :last_error, :text unless column_exists?(:project_mirror_data, :last_error)
+  end
+
+  def down
+    # db/migrate/20180502122856_create_project_mirror_data.rb will remove the table
+  end
+end