The limit for the meta space on /opt/opennms/bin/opennms is too low

The PermGen is a concept that has been deprecated in Java 8.

The new equivalent is the meta space. In theory, there is no need to limit that space, but I found that there is a hard limit on the opennms init script that clamps the meta space to 256MB:

if [ `echo "$ADDITIONAL_MANAGER_OPTIONS" | grep -c MaxMetaspaceSize=` -eq 0 ]; then
    ADDITIONAL_MANAGER_OPTIONS="$ADDITIONAL_MANAGER_OPTIONS -XX:MaxMetaspaceSize=256m"
fi

I think that number is too low, as I found some meta space problems on a customer site.

If we're planning to keep that limitation, we should increase the number to at least 512MB.