testsuite: make stap_run[23] more verbose when failing

testsuite: make stap_run[23] more verbose when failing

If a stap_run[23] test case fails, in that the actual output varies
from the expected output, all remaining actual output lines were
neither compared nor reported in systemtap.log.

* testsuite/lib/stap_run2.exp (stap_run3): In case of a line mismatch,
  report any remaining actual lines.