virgl/ci: Setup virtio-vsock based IPC

The virtio transport for virtual sockets (virtio-vsock) improves the communication between the tasks executed in a crosvm guest context and the monitor process that runs on the job runner.

The old approach relies on using regular files, which is potentially unreliable because the data cannot be transferred in real-time and there is no possibility to properly terminate the transmission. Additionally, it requires a forced sleep for syncing content, while the minimum amount of time necessary to wait cannot be easily and safely determined.

As an additional optimization, ensure the Mesa Shader Cache is stored on a tmpfs mount point. This reduces the tests execution duration by 2-3 %, while preventing several hundreds of megabytes to be written on the storage media (per job run).

Signed-off-by: Cristian Ciocaltea cristian.ciocaltea@collabora.com