ported x86_64 python tests to be compatible with aarch64

[ramyak-mehra]

Added support to pull and set aach64 images Changed how vcpus are checked. This is done because on aarch64 /proc/cpuinfo doesn't directly return the number of cpus.

Signed-off-by: Ramyak mehra rmehra_be19@thapar.edu

Summary of the PR

Please summarize here why the changes in this PR are needed.

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• [x] All commits in this PR are signed (with git commit -s), and the commit message has max 60 characters for the summary and max 75 characters for each description line.
• [x] All added/changed functionality has a corresponding unit/integration test.
• [x] Any newly added unsafe code is properly documented.

[andreeaflorescu]

We also need to run the tests on aarch64 by adding the platform tag here: https://github.com/rust-vmm/vmm-reference/blob/93675f0891a707fc62855400509c8c9be3379bfe/.buildkite/custom-tests.json#L7