Add support for Memory Balloon

[WenceyWang]

Some of vm have a mechanism called memory balloon which will reduce the available memory amount while they are not in use. And these memory will be usable while use it.
And winrun4j will read available memory amount and use this number to start java, which cause most of memory become unusable.
I think there should be a switch in INI file that let winrun4j ignore available memory amount and start java by the vm.heapsize.preferred .