FFI: tests: add a oom_score_adj test

[bilelmoussaoui]

We would need a new test that covers the following:

• the systemd service unit file sets a OOMScoreAdjust= property value higher than the default score in the QM service (but lower than ASIL B score)

• the correct values are set in the kernel by reading the sysfs entries

[dougsland]

We would need a new test that covers the following:

• the systemd service unit file sets a OOMScoreAdjust= property value higher than the default score in the QM service (but lower than ASIL B score)
• the correct values are set in the kernel by reading the sysfs entries

Thanks @bilelmoussaoui. We will add this one in our list too.