@VisibleForTesting
  public QueueConnectionImpl promoteBackupToPrimary(List<Connection> backups) {
    QueueConnectionImpl primary = null;
    for (int i = 0; primary == null && i < backups.size(); i++) {
      QueueConnectionImpl lastConnection = (QueueConnectionImpl) backups.get(i);
      if (promoteBackupCnxToPrimary(lastConnection)) {
        primary = lastConnection;
      }
    }
    return primary;
  }
Make sure that we have enough backup servers.

Add any servers we fail to connect to to the excluded servers list.
geode-core/src/main/java/org/apache/geode/cache/client/internal/QueueManagerImpl.java