Keep sync running if some connections have a problem

[wonder-sk]

Right now, if there are multiple connections defined and one of them fails to sync for some reason, the whole sync stops. It would be nice if db-sync tool would be less strict and it could tolerate some failing connections.

[JanCaha]

This issue should be solved by changes introduced in #104. Failing individual syncs should not cause complete stop of the deamon.

This is true as long as these fails are not caused by failed init of the connection. We could probably work around failed inits if that should be the case ...