Fix nvme instance storage discovery

[Ivaylogi98]

Refactor NVMe instance storage discovery to be IaaS-agnostic

Refactors #396 to address review feedback from @rkoster.

What changed from #396

IaaS-agnostic design — the AWS-specific awsNVMeInstanceStorageResolver and its hardcoded EBS pattern are replaced by a generic SymlinkDeviceResolver in infrastructure/devicepathresolver. The managed volume
pattern (/dev/disk/by-id/nvme-Amazon_Elastic_Block_Store_) and device pattern (/dev/nvmen1) are passed in entirely via agent config (InstanceStorageManagedVolumePattern, InstanceStorageDevicePattern), set by
the stemcell builder's bosh_aws_agent_settings stage — not hardcoded in the resolver.

udev race condition fixed — the original PR globbed /dev/disk/by-id/ symlinks without waiting for udev to finish creating them. On fast boots, this returned 0 EBS symlinks, causing all NVMe devices (including
the root EBS volume) to be misidentified as instance storage. udevadm trigger + udevadm settle are now called before globbing.

Unit tests fixed — all compilation errors and test failures from #396 are resolved.

Algorithm

1. Glob all NVMe devices: /dev/nvme*n1
2. Run udevadm trigger + udevadm settle
3. Glob EBS symlinks via InstanceStorageManagedVolumePattern
4. Resolve each symlink to its target device
5. Subtract EBS devices from all NVMe → remainder is instance storage
6. Partition only the discovered instance storage devices

Verified using m6id.large

Enabled raw_instance_storage: true

3 NVMe devices present:

• /dev/nvme0n1 — root EBS (5G) → correctly excluded
• /dev/nvme1n1 — ephemeral EBS (50G) → correctly excluded
• /dev/nvme2n1 — instance storage (118G) → correctly discovered and set up as raw ephemeral

Used Claude Code

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