Fix windows NodePublish failing because mount target doesn't exist

[wongma7]

Is this a bug fix or adding new feature? /bug

What is this PR about? / Why do we need it? on windows it is normal for the mount target not to exist. Added comment:

// Do not return os.IsNotExist error. Other errors were handled above. It is
// the responsibility of the caller to check whether the given target path
// exists (in Linux, the target mount directory must exist before mount is
// called on it) or not (in Windows, the target must NOT exist before a
// symlink is created at it)

What testing is done? tested on my EKS 1.20 cluster

Built image

OUTPUT_TYPE=registry OS=windows OSVERSION=1809 TAG=oct6-0 REGISTRY=x.dkr.ecr.us-west-2.amazonaws.com make image

Edited the daemonset to use my image and bump verbosity to 5
k edit daemonset ebs-csi-node-windows -n kube-system

Scaled my windows deployment up

k scale deployment windows-server-iis --replicas 1

Checked my volume is readable.

k exec -it windows-server-iis-7c5fc8f6c5-9rfhz powershell
Windows PowerShell
Copyright (C) Microsoft Corporation. All rights reserved. 

PS C:\> ls data 


    Directory: C:\data 


Mode                LastWriteTime         Length Name
----                -------------         ------ ----
-a----         7/8/2021   8:05 PM              3 testfile1.txt

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: wongma7

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[nirmalaagash]

/lgtm

[wongma7]

/test pull-aws-ebs-csi-driver-verify