test/system: log socat output in retry loop

This test is currently flaking with the latest pasta update[1]. As part
of debugging this it was hard to see why socat fails 5 times in this
loop as the run function does not log the output so I had to add an echo
here.

[1] https://bugs.passt.top/show_bug.cgi?id=202

Signed-off-by: Paul Holzinger <pholzing@redhat.com>