docs: Add E2E testing guide and prerequisites

[williamzujkowski]

Summary

End-to-end testing of moltdown requires specific host prerequisites that may not be available in all environments.

Prerequisites Required

1. Passwordless sudo for libvirt operations:

   • Starting/stopping VMs
   • Managing snapshots
   • Network configuration

2. libvirtd service running:

   sudo systemctl start libvirtd
   sudo systemctl enable libvirtd

3. Required packages:

   sudo apt install genisoimage qemu-kvm libvirt-daemon-system

4. User in libvirt group:

   sudo usermod -aG libvirt $USER

Test Checklist

Manual E2E test checklist for contributors:

• Prerequisites check passes
• ISO generation works
• VM creation succeeds
• Autoinstall completes (~10-15 min)
• SSH access works with configured credentials
• Bootstrap script completes all phases
• Snapshot create/revert works
• Cleanup removes all artifacts

Automated Testing

For CI/CD integration testing, we need:

• Nested virtualization support (GitHub Actions doesn't support this)
• Alternative: Use self-hosted runners with KVM support

Related: #5 (Integration tests with actual VM creation)