CLOUDSTACK-5927. Storage garbage collector is trying to destroy the SSVM/CPVM root disk that is in use.
In case of VMware VM during root volume preparation if we are switching to a new volume, force expunge root disk that was created from the old template.
Because otherwise storage garbage collector will later try to expunge the old disk marked for expunge and fail with 'Cannot delete file' exception
since in VMware the new root vmdk has the same name and is now in use.