Cover the case where @netauto would be used to create the command line in virStorageBackendFileSystemMountCmd. Essentially when the pool type is "netfs", but the "source.format" is empty, create the command line properly. Signed-off-by: John Ferlan <jferlan@redhat.com> ACKed-by: Michal Privoznik <mprivozn@redhat.com>