Add command cluster get-failure-domain

[zymap]

Master issue: #2

output example:

➜  pulsarctl git:(clusters_get_failure_domain) ./pulsarctl cluster get-failure-domain -h
USED FOR:
    This command is used for getting the specified failure domain on the specified cluster.

REQUIRED PERMISSION:
    This command requires super-user permissions.

EXAMPLES:
    #getting the broker list in the <cluster-name> cluster failure domain <domain-name>
    pulsarctl clusters get-failure-domain -n <domain-name> <cluster-name>

OUTPUT:
    #output example
    {
      "brokers" : [
        "failure-broker-A",
        "failure-broker-B",
      ]
    }

    #the cluster name is not specified or the cluster name is specified more than one
    [✖]  only one argument is allowed to be used as a name

    #the specified cluster does not exist in the broker
    [✖]  code: 404 reason: Cluster does not exist

Usage: pulsarctl clusters get-failure-domain [flags]

Aliases: get-failure-domain, gfd

FailureDomain flags:
  -n, --domain-name string   The failure domain name

Common flags:
  -s, --admin-service-url string   The admin web service url that pulsarctl connects to. (default "http://localhost:8080")
  -C, --color string               toggle colorized logs (true,false,fabulous) (default "true")
  -h, --help                       help for this command
  -v, --verbose int                set log level, use 0 to silence, 4 for debugging (default 3)

Use 'pulsarctl clusters get-failure-domain [command] --help' for more information about a command.

[sijie]

what are the error cases?

[zymap]

args error and cluster not found error