test-clone: fix some instability in pooled clone race condition test
Healthy output (one log file mentioning "existing pooled" and one
mentioning "new pooled") will now print in a stable order, but
unhealthy output will print some sort of error.
This reduces the flakiness of the test from 55% to 38%. My next patch
makes it completely stable.
#require docutils gettext
$ $TESTDIR/check-gendoc zh_CN
checking for parse errors