Server management

Eg.
```sh
# krctl server ls
NAME     URL 
plato       http://plato:5000

# krctl server create --name tulip --url http://tulip:5000 --auth basic --username test --password testpass
Server created, testing...
Server successfully connected.

# krctl server rm plato
Do you want to remove 'plato'? [Y/n] n
Exiting.

# krctl system info --server plato
--- info bout plato
```