tests: fix spurious failure for awk implementation of TAP driver

tests: fix spurious failure for awk implementation of TAP driver

* tests/tap-realtime.test: The awk+shell implementation of the TAP
driver must "read ahead" of one line in order to catch the exit
status of the test script it runs.  So, in the TAP-producer script
here, be sure to echo one "dummy" line after each TAP result line
in order not to cause false positives.