Make auto-cancelling pending pipelines on by default

changelogs/unreleased/enable-auto-cancelling-by-default.yml

+---
+title: Enable cancelling non-HEAD pending pipelines by default for all projects
+merge_request: 11023
+author:

db/migrate/20170502065653_make_auto_cancel_pending_pipelines_on_by_default.rb

+class MakeAutoCancelPendingPipelinesOnByDefault < ActiveRecord::Migration
+  include Gitlab::Database::MigrationHelpers
+
+  DOWNTIME = false
+
+  def up
+    change_column_default(:projects, :auto_cancel_pending_pipelines, 1)
+  end
+
+  def down
+    change_column_default(:projects, :auto_cancel_pending_pipelines, 0)
+  end
+end

db/migrate/20170502070007_enable_auto_cancel_pending_pipelines_for_all.rb

+class EnableAutoCancelPendingPipelinesForAll < ActiveRecord::Migration
+  include Gitlab::Database::MigrationHelpers
+
+  DOWNTIME = false
+
+  def up
+    connection.execute(
+      'UPDATE projects SET auto_cancel_pending_pipelines = 1')
+  end
+
+  def down
+    # Nothing we can do!
+  end
+end

db/schema.rb

@@ -986,7 +986,7 @@ ActiveRecord::Schema.define(version: 20170508190732) do
     t.text "description_html"
     t.boolean "only_allow_merge_if_all_discussions_are_resolved"
     t.boolean "printing_merge_request_link_enabled", default: true, null: false
-    t.integer "auto_cancel_pending_pipelines", default: 0, null: false
+    t.integer "auto_cancel_pending_pipelines", default: 1, null: false
     t.string "import_jid"
     t.integer "cached_markdown_version"
     t.datetime "last_repository_updated_at"