Continue to Payment button is not accessible

When a user starts the payment/verification flow.
Tab navigation skips past the "Continue to Payment" button

ECOM-1302

lms/static/js/spec/verify_student/make_payment_step_view_spec.js

@@ -103,9 +103,10 @@ define([
                 expect($el.length).toEqual(_.size(buttons));
                 _.each(buttons, function( expectedText, expectedId ) {
                     var buttonEl = $( '#' + expectedId );
+                    buttonEl.removeAttr('disabled');
                     expect( buttonEl.length ).toEqual( 1 );
                     expect( buttonEl[0] ).toHaveClass( 'payment-button' );
-                    expect( buttonEl[0].text ).toEqual( expectedText );
+                    expect( buttonEl[0] ).toHaveText( expectedText );
                     buttonEl[0].click();
                     expect(requests[requests.length - 1].requestBody.split('&')).toContain('processor=' + expectedId);
                 });

lms/static/js/verify_student/views/make_payment_step_view.js

@@ -58,7 +58,7 @@ var edx = edx || {};
         _getPaymentButtonHtml: function(processorName) {
             var self = this;
             return _.template(
-                '<a class="next action-primary payment-button" id="<%- name %>" tab-index="0"><%- text %></a> '
+                '<button class="next action-primary payment-button" id="<%- name %>" ><%- text %></button> '
             )({name: processorName, text: self._getPaymentButtonText(processorName)});
         },