VMware ESX hosts also use different create and extent types for flat
files, respectively "vmfs" and "VMFS".  This is not documented, but it
can be found at http://kb.vmware.com/kb/10002511

 (Recreating a missing
virtual machine disk (VMDK) descriptor file).

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Fam Zheng <famz@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>