db:migrate:up and db:migrate:down don't use transactions

While db:migrate and db:rollback both wrap changes into transactions if database engine supports DDL transactions, db:migrate:up and db:migrate:down don't even try to detect if engine supports this.

Also, the code which handles this is not really very DRY.

up/down tasks are using this piece of code:

    def run
      target = migrations.detect { |m| m.version == @target_version }
      raise UnknownMigrationVersionError.new(@target_version) if target.nil?
      unless (up? && migrated.include?(target.version.to_i)) || (down? && !migrated.include?(target.version.to_i))
        target.migrate(@direction)
        record_version_state_after_migrating(target.version)
      end
    end

migrate/rollback tasks are using this one:

    def migrate
      current = migrations.detect { |m| m.version == current_version }
      target = migrations.detect { |m| m.version == @target_version }

      if target.nil? && !@target_version.nil? && @target_version > 0
        raise UnknownMigrationVersionError.new(@target_version)
      end
...
        # On our way up, we skip migrating the ones we've already migrated
        next if up? && migrated.include?(migration.version.to_i)

        # On our way down, we skip reverting the ones we've never migrated
        if down? && !migrated.include?(migration.version.to_i)
          migration.announce 'never migrated, skipping'; migration.write
          next
        end

        begin
          ddl_transaction do
            migration.migrate(@direction)
            record_version_state_after_migrating(migration.version)
          end
        rescue => e
...

Need to:

• make both up/down and migrate/rollback use the same method

• ensure up/down/migrate/rollback tasks are using ddl_transaction wrapper

• backport to 2.x since it is also affected