refactor LibvirtStorageAdoptor#createDiskFromTemplate to shape up
correct the wrong physical disk directory pass
change qemu-img info output format to get acurate disk size

change output format from human to json
bugfix: set disk size parameter
bugfix: correct QemuImg#info comment
Feature: add sparse mode support (hard coding)
make volume provisioning type configurable
bugfix: volume creation format specification bug
make disk provisioning type configurable from disk offering
bugfix: enum conversion bug
add provisioning type to volumes_view
alter disk offering view to support provisioning type
make disk|service offering API return a provisioning type
bugfix: createServiceOffering doesn't work
add UI to display and configure provisioning type of a volume