Description of problem:
vol-create-as format is lack of qed

Version-Release number of selected component (if applicable):
libvirt-0.9.10-21.el6.x86_64

How reproducible:
100%

Steps to Reproduce:
# man virsh
  vol-create-as pool-or-uuid name capacity [--allocation size] [--format
       string] [--backing-vol vol-name-or-key-or-path] [--backing-vol-format
       string]
           Create a volume from a set of arguments.  pool-or-uuid is the name
           or UUID of the storage pool to create the volume in.  name is the
           name of the new volume.  capacity is the size of the volume to be
           created, as a scaled integer (see NOTES above), defaulting to bytes
           if there is no suffix.  --allocation size is the initial size to be
           allocated in the volume, also as a scaled integer defaulting to
           bytes.  --format string is used in file based storage pools to
           specify the volume file format to use; raw, bochs, qcow, qcow2,  ----> need add vmdk and qed
           vmdk.  --backing-vol vol-name-or-key-or-path is the source backing
           volume to be used if taking a snapshot of an existing volume.
           --backing-vol-format string is the format of the snapshot backing
           volume; raw, bochs, qcow, qcow2, vmdk, host_device.       ------> need add qed


Actual results:
vol-create-as format is lack of qed and vmdk

Expected results:
Add qed and vmdk

Additional info: