Allow config to sync even if NVT family is not available

[mattmundell]

What:

When syncing a config from the feed and the NVTs do not yet exist, then sync the config anyway with "" as family.

Why:

Configs sync should succeed even if the NVTs aren't synced.

How:

DELETE FROM nvts;
Delete feed config Discovery.
Empty trash.
Discovery should auto sync.
select * from nvt_selectors where name = '74b247ae-d1fc-4105-99e2-01125889b4eb';
Should be no families.
delete from meta where name = 'nvts_feed_version' or name = 'nvts_check_time';
Wait for NVTs to sync.
select * from nvt_selectors where name = '74b247ae-d1fc-4105-99e2-01125889b4eb';
Should now have families.

Checklist:

• Tests
• CHANGELOG Entry