Implement tests for lo2s

[cvonelm]

Due to the nature of perf and all the other interfaces we are using, lo2s is a rather hard software to test in in isolated set-up.

However, in the past I have run pretty often into breakages that could have been discovered by simple tests.

lo2s should atleast have a make test command that allows someone to verify locally if we had any major breakages.

Beyond that, I feel that even in a locked down VM such as GitHub provides, simple smell tests such as lo2s -- sleep 10 should be able to run.

Further steps:

• implement a basic set of tests, parameterized by perf_event_paranoid level, debugfs availability, ..., in CTest in lo2s
• investigate the possiblity of custom GitHub runners that allows us to run tests in an environment that we can control effectively (maybe using elab systems? This might be useful for other energy group tools too)
• OR, investigate how much perf is possible in a GitHub VM