i found a solution for confirming a delivery order from sale order confirm button.Here i shared the code for achieving this,

Inherit a existing workflow and add a follwong lines,

                picking = stock_pick_obj.browse(cr, uid, pick_id)
                wf_service = netsvc.LocalService("workflow")
                wf_service.trg_validate(uid, 'stock.picking', picking.id, 'button_confirm', cr)
                self.pool.get('stock.move').force_assign(cr, uid, move_idds)
                wf_service.trg_write(uid, 'stock.picking',picking.id, cr)
                self.pool.get('stock.picking').action_move(cr, uid, [picking.id], context=context)
                wf_service.trg_validate(uid, 'stock.picking', picking.id, 'button_done', cr)

Give any other solutions if you have to achieve better than this.

Thanks.