Updated basket page button handling

Pulling the processor name from the data attribute instead of the value attribute. It is unclear if the value attribute works as expected for button elements. Given that we know data attributes definitely work, we will use it.

ECOM-6155

ecommerce/static/js/pages/basket_page.js

@@ -85,7 +85,7 @@ define([
                 var $btn = $(e.target),
                     deferred = new $.Deferred(),
                     promise = deferred.promise(),
-                    paymentProcessor = $btn.val(),
+                    paymentProcessor = $btn.data('processor-name'),
                     data = {
                         basket_id: basketId,
                         payment_processor: paymentProcessor

ecommerce/templates/oscar/basket/partials/basket_content.html

@@ -229,10 +229,9 @@
                             <button data-track-type="click"
                                     data-track-event="edx.bi.ecommerce.basket.payment_selected"
                                     data-track-category="checkout"
-                                    data-processor-name="{{ processor.NAME }}"
+                                    data-processor-name="{{ processor.NAME|lower }}"
                                     data-course-id="{{ course.id }}"
                                     class="btn payment-button"
-                                    value="{{ processor.NAME|lower }}"
                                     id="{{ processor.NAME|lower }}">
                                 {% if processor.NAME == 'cybersource' %}
                                     {% trans "Checkout" %}