MembershipInformation oldDSMembershipInfo() {
    if (quorumChecker != null) {
      return quorumChecker.getMembershipInfo();
    }
    return null;
  }
returns the membership socket of the old distributed system, if available, when
isReconnectingDS returns true. This is used to connect the new DM to the distributed system
through RemoteTransportConfig.
geode-core/src/main/java/org/apache/geode/distributed/internal/InternalDistributedSystem.java