Use querySelector to click the correct HTML element

#140 (comment)
notes that the same change was used in core so that the HTMLUnit code
does not care about the type of the element being clicked.

Author: MarkEWaite

src/test/java/org/jenkinsci/plugins/docker/commons/credentials/DockerServerCredentialsTest.java

@@ -35,7 +35,6 @@
 import org.htmlunit.html.HtmlForm;
 import hudson.security.ACL;
 import hudson.util.Secret;
-import hudson.util.VersionNumber;
 import org.junit.Rule;
 import org.junit.Test;
 import org.jvnet.hudson.test.JenkinsRule;
@@ -95,17 +94,9 @@ public void configRoundTripUpdateCertificates() throws Exception {
         store.addDomain(domain, credentials);
 
         HtmlForm form = getUpdateForm(domain, credentials);
-        for (HtmlElement button : form.getElementsByAttribute("input", "class", "secret-update-btn")) {
-            button.click();
-        }
+        ((HtmlElement) form.querySelector(".secret-update-btn")).click();
 
-        if (j.jenkins.getVersion().isOlderThan(new VersionNumber("2.413"))) {
-            /* Jenkins 2.412 and earlier use a text area for the client key */
-            form.getTextAreaByName("_.clientKeySecret").setText("new key");
-        } else {
-            /* Jenkins 2.413 and newer use an input field for the client key */
-            form.getInputByName("_.clientKeySecret").setValue("new key");
-        }
+        form.getTextAreaByName("_.clientKeySecret").setText("new key");
         form.getTextAreaByName("_.clientCertificate").setText("new cert");
         form.getTextAreaByName("_.serverCaCertificate").setText("new ca cert");
         j.submit(form);