Don't validate RDAP nameserver names using validateDomainName

The nameserver may be external, in which case its TLD will not appear in our
list of valid TLDs, and the search will be rejected erroneously.

Tests for letter case canonicalizations also added at reviewer's suggestion.

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=171985702

java/google/registry/rdap/RdapNameserverAction.java

@@ -14,15 +14,18 @@
 
 package google.registry.rdap;
 
+import static google.registry.flows.host.HostFlowUtils.validateHostName;
 import static google.registry.model.EppResourceUtils.loadByForeignKey;
 import static google.registry.request.Action.Method.GET;
 import static google.registry.request.Action.Method.HEAD;
 import static google.registry.util.DateTimeUtils.START_OF_TIME;
 
 import com.google.common.collect.ImmutableMap;
+import google.registry.flows.EppException;
 import google.registry.model.host.HostResource;
 import google.registry.rdap.RdapJsonFormatter.OutputDataType;
 import google.registry.request.Action;
+import google.registry.request.HttpException.BadRequestException;
 import google.registry.request.HttpException.NotFoundException;
 import google.registry.request.auth.Auth;
 import google.registry.util.Clock;
@@ -59,7 +62,14 @@ public class RdapNameserverAction extends RdapActionBase {
     DateTime now = clock.nowUtc();
     pathSearchString = canonicalizeName(pathSearchString);
     // The RDAP syntax is /rdap/nameserver/ns1.mydomain.com.
-    validateDomainName(pathSearchString);
+    try {
+      validateHostName(pathSearchString);
+    } catch (EppException e) {
+      throw new BadRequestException(
+          String.format(
+              "%s is not a valid %s: %s",
+              pathSearchString, getHumanReadableObjectTypeName(), e.getMessage()));
+    }
     // If there are no undeleted nameservers with the given name, the foreign key should point to
     // the most recently deleted one.
     HostResource hostResource =