lib/tests/Makefile.am: Clean up after test_run_id

Add test_run_id.persist- and test_run_id.persist to CLEANFILES. While
the second one should be automatically cleaned up by the test case, we
leave that in here too, for good measures. And make clean should clean
up after a failed test run, too, anyway.

Signed-off-by: Gergely Nagy <algernon@balabit.hu>