virttest.cartesian_config: Make 'replace deprecated template with eval in cart-config' works for multi deprecated template

        - rebase:
            type = qemu_disk_img_rebase
            rebase_mode = safe
            base_format = qcow2
            guest_file_name_image1 = "${tmp_dir}/base"
            image_chain += " snA snB"
            image_name_snA = "images/snA"
            image_name_snB = "images/snB"
            guest_file_name_snA = "${tmp_dir}/snA"
            guest_file_name_snB = "${tmp_dir}/snB"
            variants:
                - snB:
                    check_files = "${tmp_dir}/base ${tmp_dir}/snA ${tmp_dir}/snB"
                    variants:
                        - to_base:
                            rebase_list = "snB > image1"

from the log we know that only signal ${tmp_dir} is replace to /var/tmp
But check_files did not change.

Signed-off-by: Feng Yang <fyang@redhat.com>