CurrentUser: Add method for getting a loggable name

This is useful for including a CurrentUser into log messages.

Change-Id: I25631902e5fb7b69960b3f53d62b51de3c70e9e2
Signed-off-by: Edwin Kempin <ekempin@google.com>

java/com/google/gerrit/server/CurrentUser.java

@@ -95,6 +95,11 @@ public abstract class CurrentUser {
     return Optional.empty();
   }
 
+  /** @return unique name of the user for logging, never {@code null} */
+  public String getLoggableName() {
+    return getUserName().orElseGet(() -> getClass().getSimpleName());
+  }
+
   /** Check if user is the IdentifiedUser */
   public boolean isIdentifiedUser() {
     return false;

java/com/google/gerrit/server/IdentifiedUser.java

@@ -323,6 +323,7 @@ public class IdentifiedUser extends CurrentUser {
   }
 
   /** @return unique name of the user for logging, never {@code null} */
+  @Override
   public String getLoggableName() {
     return getUserName()
         .orElseGet(