get_allotted doesn't get the list of nic names, only the # of nics
allowed to the user.  We check the db_file later for existing
number of nics.

Also close the conf file on success, and print filename and errno
if we failed to open conf file.
Signed-off-by: Serge Hallyn <serge.hallyn@ubuntu.com>
Acked-by: Stéphane Graber <stgraber@ubuntu.com>