MAGETWO-59893: Email Associated with PayPal Merchant Account Adaptation for On-Boarding

- Fix integration test

Author: viktym

dev/tests/integration/testsuite/Magento/Paypal/Model/Config/Structure/Reader/_files/expected/config.xml

@@ -593,7 +593,8 @@
                         <label>Express Checkout</label>
                         <frontend_model>Magento\Paypal\Block\Adminhtml\System\Config\Fieldset\Expanded</frontend_model>
                         <field id="business_account" translate="label comment tooltip" showInDefault="1" showInWebsite="1" sortOrder="5">
-                            <label>Email Associated with PayPal Merchant Account</label>
+                            <label>Email Associated with PayPal Merchant Account (Optional)</label>
+                            <frontend_class>not-required</frontend_class>
                             <comment>
                                 <![CDATA[<a href="http://www.magentocommerce.com/paypal">Start accepting payments via PayPal!</a>]]>
                             </comment>