### summary:
cluster_manager stop working and whole cluster stopped service.
### environment：
CentOS7.6
mcu server: 4.3.x
### steps:
1. two cluster_managers: A for master, B for slave
2. network flash，B became master,
3. network recover, A & B both master, B life_time is shorter, so B process exit.
4. rabbitmq queue "owt-cluster" deleted. so A can not received any message from queue "owt-cluster", all other service lost connection with cluster_manager
### reason:
amqp_client.js:157
```
handler.close = function() { request_q && request_q.destroy(); request_q = undefined; exc && exc.destroy(true); exc = undefined; };
```
the handler.close will called if cluster_manager process exited by calling "process.exit(1);"
and request_q.destroy() will delete the queue even if the other cluster_manager still connected on it.
### manually reproduce:
start master cluster_manager A.
modify slave cluster_manager B file: clusterManager.js at last lines for simulate
```
exports.run = function (topicChannel, clusterName, id, spec) { var manager = new ClusterManager(clusterName, id, spec); runAsCandidate(topicChannel, manager); //just using runAsMaster(topicChannel, manager); instead };
```
start cluster_manager B.
cluster_manager B detected "Double master" and exit.
cluster_manager A stopped service.
### suggestion:
request_q.destroy(); using option: request_q.destroy({ifUnused : true});
