kvm: Use libvirt-java 0.5.1

This version is Java 6 compatible and makes CloudStack Java 6
compatible again
add missing jna-4.0.0.jar to cloudstack-agent library by changing scope from provided to default runtime
Don't check implementation version of Object for DatabaseUpgradeChecker
Cloudstack-2997: the maxconn setting is masked by wrong conditions
resolve conflicts of Toshiaki Hatano (haeena)'s vxlan branch