Optimization suggestions for add hosts

[cooper-lzy]

Since we need to register the storaged node through add hosts, it is recommended to add a command to view the host_list that has been communicating with meta but has not been registered. This will facilitate user registration.

[darionyaphet]

If the host not registed into meta service, it will not be saved. So it seems could not be distinguish

[darionyaphet]

maybe we should support another command to display which hosts have be added into the machine list. It's more useful.

[Sophie-Xie]

@MuYiYong @darionyaphet talked it offline, it will not be change in v3.x.