jstat tests doesn't tolerate dash in the O column

When running jstat tests like the following:
test/jdk/sun/tools/jstatd/TestJstatdServer.java

with Generational ZGC we get a failure because the O (old generation percentage) is reported as `-` and not a number. The reason why it is reported as `-` is that the current capacity of the old generation is zero and that leads to a divide-by-zero in this line:
https://github.com/openjdk/jdk/blob/82a8e91ef7c3b397f9cce3854722cfe4bace6f2e/src/jdk.jcmd/share/classes/sun/tools/jstat/resources/jstat_options#L1029

G1 has some workarounds for this situation where the reported capacity is slightly above 0. I'm a bit reluctant to add such a hack into Generational ZGC. I've talked to the jstat maintainers and they propose that we simply relax the test.