How to limit the search whiel searching for VM Folders or VMs in a vCenters out of several vCenters?

Hi Guys,

I have several vCenters in the vRO inventory and it is expected that one more vCenters may not be reachable at times (Disaster Recovery scenario) and when use the vCenter API what collects everything based on object type the script fails as the VMs or VM Folders or not accessible on the vcenter that is down/not reachable.

vms = VcPlugin.getAllVirtualMachines();

So how I can restrict this search for a specific vcenter VMs or VM Folders?