CLOUDSTACK-4549: Do not force RBD snapshot backups to RAW format

Since we use qemu-img to copy from RBD to Secondary Storage we no
longer have to force to RAW images, but can stick with QCOW2

When the snapshot backups are QCOW2 format they can easily be deployed
again when restoring from a backup

Conflicts:

	plugins/hypervisors/kvm/src/com/cloud/hypervisor/kvm/storage/LibvirtStorageAdaptor.java
CLOUDSTACK-6535: IAM:MS:API createVMSnapshot doesn't preserve access
rights.