CLOUDSTACK-6079 suppress updates of public traffic type's broadcast type if traffic type is not public

fixed issue: if public traffic is on a physical network isolated by VLAN,
and guest traffic is on an another physical network isolated by VXLAN,
public traffic's broadcast type is updated to VXLAN by mistake.
CLOUDSTACK-6072 bugfix: vxlan networks not deallocating vnet ids

made GuestNetworkGuru release VNI during network shutdown.
rename ImageFormat#thinProvisioned -> ImageFormat#supportThinProvisioning
Add preallocation column to the volumes table
add a test case to test qemu-img with preallocation option
add provisionType parameter to createDiskFromTemplate method
fix VolumeObject class to reflect the change in Volume class
add "ProvisioningType" member to DiskProfile
add 'ProvisioningType' member to VolumeObjectTO
make provisioningType constructor parameter mandatory in VolumeVO class
define Preallocation enum
set preallocation option as qemu-img option
make DataDisk sparse ready
set provisioningType in allocVolume method
refactor LibVirtStorageAdaptor#createPhysicalDisk
replace libvirt by qemu-img for volume creation

to support preallocation option
refactor LibvirtStorageAdoptor#createDiskFromTemplate to shape up
change qemu-img info output format to get acurate disk size

change output format from human to json
Feature: add sparse mode support (hard coding)
make volume provisioning type configurable