fix: mount options for fsGroup delegation must ensure RWX for the group

[mpatlasov]

If user sets fsGroup: <gid> in Pod's spec.securityContext, kubelet delegate fsGroup to CSI Driver, and NodeStageVolume() adds gid=<gid> to mount options. This might be not enough to make volume writable for the user:

$ kubectl exec fedora -- ls -ld /mnt/claim
drwxr-xr-x. 2 root 1002 0 Sep 13 12:04 /mnt/claim
$ kubectl exec fedora -- touch /mnt/claim/FILE
touch: cannot touch '/mnt/claim/FILE': Permission denied

/kind bug

Fixes #835

Release note:

none

[k8s-ci-robot]

Hi @mpatlasov. Thanks for your PR.

I'm waiting for a kubernetes-csi member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

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[coveralls]

Pull Request Test Coverage Report for Build 11385152781

Details

• 20 of 20 (100.0%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.5%) to 79.327%

---

Totals
Change from base Build 11310197804:	0.5%
Covered Lines:	1013
Relevant Lines:	1277

---

💛 - Coveralls

[andyzhangx]

/ok-to-test

[andyzhangx]

/retest

[andyzhangx]

/retest

[mpatlasov]

Last force-push: fixed spelling in nodeserver_test.go (s/rasing/raising)

[mpatlasov]

/test pull-csi-driver-smb-e2e-windows-2019

[andyzhangx]

/lgtm

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

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

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[andyzhangx]

/retest