Add missing migration for minimal Project build_timeout

db/post_migrate/20180507083701_set_minimal_project_build_timeout.rb

+class SetMinimalProjectBuildTimeout < ActiveRecord::Migration
+  include Gitlab::Database::MigrationHelpers
+
+  DOWNTIME = false
+  MINIMUM_TIMEOUT = 600
+
+  # Allow this migration to resume if it fails partway through
+  disable_ddl_transaction!
+
+  def up
+    update_column_in_batches(:projects, :build_timeout, MINIMUM_TIMEOUT) do |table, query|
+      query.where(table[:build_timeout].lt(MINIMUM_TIMEOUT))
+    end
+  end
+
+  def down
+    # no-op
+  end
+end