This is needed for the next commit.
Also, it doesn't really test anything novel. wait_for_debug_log is
inherently racy, so will randomly terminate at the exact point or later.
So the randomization is already sufficiently covered by the existing
test.
This test sporadically fails due to the Python test missing log lines
for reasons that are poorly understood. The problem is made worse by the
fact that this test does not retain the log files from iteration to
iteration.
Change the test to do logline detection in a more robust manner (by
using `re.search` on the whole log content) in a way that is comparable
to the existing `assert_debug_log` utility, and retain all debug.log
content from case to case.
This part of the test sporadically fails on CI infrastructure. Instead
of perturbing a single .ldb file of each type, move all .ldb files of a
given type to ensure a bad startup.
