Add PVH related integration tests

[roypat]

Adds PVH related integration tests, such as

• ~~FreeBSD boots successfully inside of firecracker~~ It does not on m6a.metal
• Linux compiled with PVH support boots successfully inside of firecracker
• ~~Linux compiled with PVH support meets boottime SLA of 150ms~~ PVH is not supported on 4.14, which is the kernel version for which we measure boottime in CI.
• Linux compiled with PVH support boots with initrd

Since the feature we are testing is "PVH boot protocol", the testing matrix we will use here is "PVH-enabled Linux".

See also https://github.com/firecracker-microvm/firecracker/issues/3041

License Acceptance

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license. For more information on following Developer Certificate of Origin and signing off your commits, please check CONTRIBUTING.md.

PR Checklist

• [ ] If a specific issue led to this PR, this PR closes the issue.
• [ ] The description of changes is clear and encompassing.
• [ ] Any required documentation changes (code and docs) are included in this PR.
• [ ] API changes follow the Runbook for Firecracker API changes.
• [ ] User-facing changes are mentioned in CHANGELOG.md.
• [ ] All added/changed functionality is tested.
• [ ] New TODOs link to an issue.
• [ ] Commits meet contribution quality standards.

---

• [ ] This functionality cannot be added in rust-vmm.

[codecov[bot]]

Codecov Report

Patch and project coverage have no change.

Comparison is base (10949af) 82.36% compared to head (4e0a489) 82.36%.

Additional details and impacted files

@@             Coverage Diff              @@
##           feature/pvh    #4073   +/-   ##
============================================
  Coverage        82.36%   82.36%           
============================================
  Files              225      225           
  Lines            28630    28630           
============================================
  Hits             23580    23580           
  Misses            5050     5050           

Flag	Coverage Δ
4.14-c7g.metal	77.75% <ø> (ø)
4.14-m5d.metal	79.68% <ø> (ø)
4.14-m6a.metal	78.80% <ø> (ø)
4.14-m6g.metal	77.75% <ø> (ø)
4.14-m6i.metal	79.67% <ø> (ø)
5.10-c7g.metal	80.66% <ø> (ø)
5.10-m5d.metal	82.33% <ø> (ø)
5.10-m6a.metal	81.55% <ø> (ø)
5.10-m6g.metal	80.66% <ø> (ø)
5.10-m6i.metal	82.32% <ø> (ø)
6.1-c7g.metal	80.66% <ø> (ø)
6.1-m5d.metal	82.33% <ø> (-0.02%)	:arrow_down:
6.1-m6a.metal	81.55% <ø> (ø)
6.1-m6g.metal	80.66% <ø> (ø)
6.1-m6i.metal	82.32% <ø> (ø)

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[roypat]

I'm putting this back into draft until the initrd issues are resolved