disable node registration when UUID is empty

[nicolehanjing]

What this PR does / why we need it:
CPI generates providerID by combining "provider_name + system UUID" e.g. "vsphere://UUID", but the system UUID we fetched from vCenter (via govmomi) is empty. So the final providerID we get is "vsphere://", which is invalid.
In such case, we should disable node registration when UUID is empty

Which issue this PR fixes (optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close that issue when PR gets merged): fixes #521

Special notes for your reviewer:

Release note:

disable node registration when UUID is empty

[k8s-ci-robot]

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[nicolehanjing]

cc @dougm @lubronzhan

[lubronzhan]

You can just error out here if vmDI has empty UUID

cloud-provider-vsphere/pkg/cloudprovider/vsphere/nodemanager.go

Line 190 in 6ba6d0e

vmDI, err := nm.shakeOutNodeIDLookup(ctx, nodeID, searchBy)

Also could you update the log here

cloud-provider-vsphere/pkg/cloudprovider/vsphere/nodemanager.go

Line 315 in 6ba6d0e

klog.V(2).Info("Hostname: ", oVM.Guest.HostName, " UUID: ", oVM.Summary.Config.Uuid)

It's still referencing the oVM.Summary.Config.Uuid to get the uuid, it will help debugging.

[lubronzhan]

/lgtm