[integ-tests] Verify the head node NFS server is configured for NFSv4-only

[hanwen-cluster]

Description of changes

• Describe what you're changing and why you're doing these changes.

Tests

• test_ebs_single has passed on all OSes

References

• This PR tests Enforce NFSv4-only on the head-node NFS server aws-parallelcluster-cookbook#3212

Checklist

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