remove VM API call dependency in azure disk WaitForAttach

[andyzhangx]

What type of PR is this?
/kind bug

What this PR does / why we need it:
This PR removes the VM API call dep in azure disk WaitForAttach func, originally devicePath is a disk LUN num, and then it could be a real device path due to the volume status update(you could find more details in this PR: #62612), in that condition, return the devicePath immediately, get disk lun num by VM API call is actually not necessary.

Which issue(s) this PR fixes:

Fixes #77462

Special notes for your reviewer:

release-note:

remove VM API call dep in azure disk WaitForAttach

/assign @feiskyer @khenidak
/priority important-soon
/sig azure

[andyzhangx]

/test pull-kubernetes-cross

[andyzhangx]

This PR works well on both Linux and Windows node.
/test pull-kubernetes-e2e-aks-engine-azure

[andyzhangx]

/hold
wait, let me add a WaitForAttach unit test tomorrow, you could still review this PR

[feiskyer]

/lgtm

[khenidak]

one nit and one big question :-)

if we make this call https://github.com/kubernetes/kubernetes/blob/master/pkg/volume/azure_dd/attacher.go#L84 return lun that was selected on VM model then our getDiskLun and WaitForAttach() would be a lot simpler, right?

[andyzhangx]

one nit and one big question :-)

if we make this call https://github.com/kubernetes/kubernetes/blob/master/pkg/volume/azure_dd/attacher.go#L84 return lun that was selected on VM model then our getDiskLun and WaitForAttach() would be a lot simpler, right?

No, the attach disk logic happens in controller manager, anyway it needs VM API call, while this PR fixed the VM API call dependency in WaitForAttach() in kubelet, originally devicePath is a disk LUN num, and then it could be a real device path due to the volume status update(you could find more details in this PR: #62612), in that condition, return the devicePath immediately, get disk lun num by VM API call is actually not necessary.

The return value of

kubernetes/pkg/volume/azure_dd/attacher.go

Line 93 in b3a73f7

return strconv.Itoa(int(lun)), err

is already LUN num, and WaitForAttach() in kubelet would return the real device path according to provided LUN num

[andyzhangx]

/test pull-kubernetes-cross
/hold cancel
I have fixed comments and added unit test for WaitForAttach func, PTAL

[feiskyer]

/test pull-kubernetes-e2e-aks-engine-azure

[feiskyer]

/lgtm
/approve

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: andyzhangx, feiskyer

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