Optimize the configuration and use of callqueue overflow trigger failover

In HADOOP-16268 implemented enable callqueue overflow trigger failover when RPC call queue is filled for hdfs router servers .

In order to configure and use parameters more conveniently, we are going to make the following optimizations:

• provide default properties for callqueue.overflow.trigger.failover such that if properties with port is not configured, we can fallback to default property (port-less)
• support refreshCallQueue to update callqueue.overflow.trigger.failover
• update callqueue.overflow.trigger.failover description information in core-site.xml