Implement a protocol of running eLinux CI tests

We already have similar logic for wxworks. vxworks_testrunner.py can be adapted for Linux tests.

QtMultimedia requires tests running on real hardware, an emulator doesn't cover all needs.
The task includes adding running on one of the devices (rpi 4/5, imx 6/8); we want to be able to easily add other devices.

The eLinux tests should be run once per day (nightly tests), and shouldn't block CI.