Recognize instance-type node label when EC2 metadata isn't available

[rifelpet]

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

What is this PR about? / Why do we need it?
This fixes volume limits on nodes that dont have the EC2 metadata endpoint available.

kOps is experiencing volume limit test failures and I believe this is because the limit is being set incorrectly.

The nodes are t3.mediums which should have a limit of 28 volumes.

The csi-node pod logs report that ec2 metadata is not available so we fallback to the metadata from the k8s API which doesn't set an instance type.

The volume limit code doesn't match the nitro regex and then defaults to the non-nitro limit of 39 volumes which is higher than the t3.medium's actual limit of 28:

aws-ebs-csi-driver/pkg/driver/node.go

Lines 681 to 691 in edb4fbe

	func (d *nodeService) getVolumesLimit() int64 {
	if d.driverOptions.volumeAttachLimit >= 0 {
	return d.driverOptions.volumeAttachLimit
	}
	ebsNitroInstanceTypeRegex := "^[cmr]5.*|t3|z1d"
	instanceType := d.metadata.GetInstanceType()
	if ok, _ := regexp.MatchString(ebsNitroInstanceTypeRegex, instanceType); ok {
	return defaultMaxEBSNitroVolumes
	}
	return defaultMaxEBSVolumes
	}

The test output confirms that it incorrectly uses a limit of 39 volumes:
Sep 12 01:37:14.436: INFO: Node ip-172-20-34-51.ap-northeast-2.compute.internal can handle 39 volumes of driver ebs.csi.aws.com

What testing is done?

[wongma7]

/lgtm
/approve

makes perfect sense, thanks.

I suppose we also ought to reduce the default from 39 to 27 (28 - 1 ENI) as I predict nitro usage will overtake non-nitro if it hasn't already. But there are still plenty of exceptions https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/volume_limits.html#instance-type-volume-limits and the ENI+EBS sharing limit is still an issue so reducing the default limit is just best-effort , we can't guarantee the limit won't get hit, even when we DO know the instance type.

[k8s-ci-robot]

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This pull-request has been approved by: rifelpet, wongma7

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