MCP: patches: AArch64: Add initial support

MCP: patches: AArch64: Add initial support

- p/fuel: classes: AArch64: virtio-pci-net sync
- p/reclass-system-salt-model: Add Armband repos

- mcp/config: AArch64: Use UEFI arm64 image
  Also, allow removal of VMs booted via guest UEFI (OVMF or AAVMF).
  While at it, bump default vCPU number from 2 to 6.

- lib.sh: AArch64: Use VGA video mode for guests
  On AArch64, there is no Cirrus video, so use VGA mode instead.
  For now, we install vgabios package no matter the arch, although
  it is only used on AArch64.
  On Debian systems, also fix a missing link for vgabios-stdvga.bin.
  Based on previous Armband work from [1].

- lib.sh: AArch64: virt-install: Use virtio-net-pci
  AArch64 virt tools (i.e. libvirt) default to "virtio-mmio", instead of
  "virtio-net-pci", at least before libvirt 3.x (see [2]).
  Without PCI bus info, we can't really enforce a specific order for
  the guest ethernet devices.
  Moreover, predictable network interface naming is out of the question
  with virtio-mmio, as there is no bus information to rely on.
  Therefore we will enforce "virtio-net-pci" on AArch64, instead of
  the default "virtio" (which translates into "virtio-mmio" currently).

- salt.sh, user-data: Add Saltstack arm64 repo

- salt.sh: Clone armband repo, apply patches from it

- classes: virtual: AArch64: virtio-pci-net sync
  Since AArch64 will be using virtio-net-pci NIC model for guests,
  predictable interface naming yields a slightly different scheme.
  Update all configuration to reflect this.

FIXME:
- Use https for fetching Armband GPG keys!
- Revise the patching mechanism, make things more dynamic.

[1] https://github.com/opnfv/armband/blob/danube.2.0/patches/fuel-library/
    arm64-bug-fixes/0002-Install-vgabios-and-link-for-aarch64.patch
[2] https://www.redhat.com/archives/libvir-list/2016-August/msg00931.html

Change-Id: If5aae22066f75732652201a78357c4931438d58d
Signed-off-by: Guillermo Herrero <Guillermo.Herrero@enea.com>
Signed-off-by: Charalampos Kominos <Charalampos.Kominos@enea.com>
Signed-off-by: Alexandru Avadanii <Alexandru.Avadanii@enea.com>