Ability to run QEMU tests in parallel

[danth]

What

With the QEMU plugin, since a port number is stored in its config file, it is not possible to run multiple integration tests in parallel.

Tests fail because only one process can listen on the chosen port at a time. Even in the test which successfully claimed the port, other parallel tests try to connect to it, which causes interference.

Acceptance Criteria (DoD)

• QEMU tests can run in parallel without any special configuration

How

Consider using a lower level interface than SSH.

Some inspiration:

• For command input, NixOS' test framework uses UNIX sockets as a serial console. I believe standard input can also be used for this.
• For file transfers, qnx_unit_tests mounts files directly into the VM rather than uploading them.

Alternatively this could be hacked around by choosing random or incremental ports, but then there is still a possibility to collide with unrelated programs.