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: NJohn Ferlan <jferlan@redhat.com>
ACKed-by: NMichal Privoznik <mprivozn@redhat.com>