shell: show which server holds the lock

fix https://github.com/chrislusf/seaweedfs/issues/1983

weed/pb/master.proto

@@ -288,6 +288,7 @@ message LeaseAdminTokenRequest {
     int64 previous_token = 1;
     int64 previous_lock_time = 2;
     string lock_name = 3;
+    string client_name = 4;
 }
 message LeaseAdminTokenResponse {
     int64 token = 1;