when new meta server is added, show it in shell command of "cluster_info"

when we run "cluster_info" in shell command, the "meta_servers" list is a static value which shows the configured meta servers when cluster is initialized:
```
>>> cluster_info
meta_servers : 10.112.3.11:30601,10.112.3.10:30601
primary_meta_server : 10.112.3.11:30601
zookeeper_hosts : 10.112.3.11:2181,10.112.3.10:2181,10.112.2.33:2181
zookeeper_root : /pegasus/c3tst-sample
meta_function_level : freezed
```

when a new meta server is added to cluster dynamically, the "meta_servers" list won't change.

shoud resolve this.

Use the cluster_info shell command as the entry point and inspect how its meta_servers field is populated. Trace that value against the cluster's dynamically added meta-server state; done means cluster_info reports newly added meta servers instead of only the initialization-time list.

Written by the indexing model from the issue text.