Support fsgroup in CSI calls; enable fsgroup e2e tests

[verult]

What type of PR is this?
/kind feature

What this PR does / why we need it:

Adds support for delegating pod fsgroup information to CSI driver. The implementation is the same as AzureFile cifs mode. Main goal is to improve test coverage of the fsgroup delegating feature by running fsgroup tests against the SMB CSI driver in k8s CSI CI.

Which issue(s) this PR fixes:

Fixes #345

Requirements:

• uses conventional commit messages
• includes documentation
• adds unit tests
• tested upgrade from previous version

Special notes for your reviewer:

Unit tests were skipped here because there was no precedence in FakeMounter to plumb out the function parameters. Let me know if you prefer to add this in.

Release note:

feat: Support fsgroup in CSI calls

/assign @andyzhangx

[coveralls]

Pull Request Test Coverage Report for Build 1498821454

• 9 of 19 (47.37%) changed or added relevant lines in 2 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage decreased (-0.8%) to 85.487%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
pkg/smb/nodeserver.go	8	18	44.44%

Totals
Change from base Build 1498314355:	-0.8%
Covered Lines:	807
Relevant Lines:	944

---

💛 - Coveralls

[andyzhangx]

/retest

[andyzhangx]

/lgtm
/approve

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

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

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• OWNERS [andyzhangx]

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