vcsim: use node id for ServiceContent.InstanceUuid
vcsim: use node id for ServiceContent.InstanceUuid

The uuid.NodeID function returns the node's (first) nic hardware address.
Using this makes ServiceContent.InstanceUuid unique, yet stable.

bruceadowns/govmomi,vmware/govmomi,bruceadowns/govmomi,bruceadowns/govmomi,vmware/govmomi,vmware/govmomi