this fix addresses the bug #1021810
Currently command 'nova-manage network list' or
'nova-manage fixed list' will return 'Command failed.' message when
there is no network defined or networks get deleted. This fix combined
with fixes to bug 1025827 will fix both command problem.
also change the print out message so that it can be translated.
code structure changes according to the suggestion from comments.
Change-Id: Id9a1a10217aac971cbbba9db5829c8478892db1a
17625dd662