Possible need of a Docker Hub repository to store container image for RISC-V CI

[endeneer]

Hi, here is a problem I'm facing while enabling rust-vmm CI for RISC-V.
Feel free to leave your suggestions. Thanks in advance.

Background:
Buildkite doesn't support RISC-V agents platform.
Therefore, I've proposed doing RISC-V CI inside QEMU running on x86_64.metal Buildkite platform (see #91).
In other words, Docker image for RISC-V CI will be very different from the existing images for x86/ARM CI.

Problem:
To accommodate such a different Docker image for RISC-V CI,
the existing Docker Hub repository rustvmm/dev cannot be reused to store the image.

Possible solutions:

1. Create a new Docker Hub repository, e.g. rustvmm/dev_riscv64 to store the image.
2. Wait until Buildkite supports RISC-V agents platform. Meanwhile, maybe RISC-V community can maintain separate GitHub fork of kvm-ioctls with RISC-V support (just like having patches accepted into RISC-V Linux kernel tree first, before merging into mainline Linux kernel).
3. Or meanwhile, manually review and accept riscv-related pull requests to rust-vmm.

[epilys]

Hello @endeneer,

Although not a CODEOWNER, this sounds completely reasonable to me. I doubt Buildkite will support RISC-V runners any time soon. As noted in #91, Github Actions have a storage limit we hit with the x86/arm64 container image; you should verify in your PR that a Github runner can build this image first, otherwise we have to find some other solution.