In vRO Javascript code, once you have an object of type VC:HostSystem, you can retrieve the host name directly with a call that looks like
// let's assume you got the variable 'host' of type VC:HostSystem
var name = host.name;
System.log("host name: " + name);
You can check in vRO API Explorer what properties/methods are available for VC:HostSystem / VcHostSystem