change 'echo' statements to logging statements testing code

I see that there are 'echo' statements in testing code, e.g. here https://gitlab.com/nunet/integration-tests/-/merge_requests/1/diffs#204ad1bb2845a482cf318defaa0258cbff5bb6f2_0_41

it may be a good idea to turn that to logging statements too, if not for the ability to pipe them through the same framework when we will start orchestrating all with Nomad, then at least in order to have them properly formatted so that to know where they come from. maybe we could even build a new logging level, say '[TEST]' in order to format all messages coming from the testing code...

@yitbarekyohannes -- what do you think?