Ensure use of "echo_i" where possible in system tests

Instead of using echo_i, some tests print output via echo "I:..., which in many instances misses test name, e.g. tsiggss:

S:tsiggss:2020-10-15T10:16:58+0200
T:tsiggss:1:A
A:tsiggss:System test tsiggss
I:tsiggss:PORTS:12408,12409,12410,12411,12412,12413,12414,12415,12416,12417
I:tsiggss:starting servers
I:testing updates to testdc1 as administrator (1)

I am not sure which branch was that but recently I saw a file with all *.log files merged (and sorted?) and it wasn't clear to which a "failed" info line belong.