Fix SimpleKdcLdapServerTests by overriding java.locale.providers (#60447)

The JDK system property makes sure date digits are always represented as ASCII chars.
This in turn helps the Kerberos response to be correctly encoded and recognised by the client.

Resolves: #57749

Author: ywangd

x-pack/qa/evil-tests/build.gradle

@@ -6,6 +6,9 @@ dependencies {
 }
 
 unitTest {
+    if (project.runtimeJavaVersion >= JavaVersion.VERSION_1_9) {
+        systemProperty 'java.locale.providers', 'COMPAT'
+    }
     systemProperty 'tests.security.manager', 'false'
     include '**/*Tests.class'
 }

x-pack/qa/evil-tests/src/test/java/org/elasticsearch/xpack/security/authc/kerberos/SimpleKdcLdapServerTests.java

@@ -11,7 +11,6 @@
 import com.unboundid.ldap.sdk.SearchScope;
 
 import org.elasticsearch.action.support.PlainActionFuture;
-import org.elasticsearch.bootstrap.JavaVersion;
 import org.elasticsearch.common.collect.Tuple;
 import org.elasticsearch.common.settings.SecureString;
 import org.elasticsearch.env.Environment;
@@ -51,9 +50,6 @@ public void testPrincipalCreationAndSearchOnLdap() throws Exception {
     }
 
     public void testClientServiceMutualAuthentication() throws PrivilegedActionException, GSSException, LoginException, ParseException {
-        assumeFalse("Java 15-ea causes issues with this test, see https://github.com/elastic/elasticsearch/issues/57749",
-            JavaVersion.current().compareTo(JavaVersion.parse("15")) >= 0);
-
         final String serviceUserName = randomFrom(serviceUserNames);
         // Client login and init token preparation
         final String clientUserName = randomFrom(clientUserNames);