[api] ignore recordnounique error while saving backend_package

there is a race going on between two processes to update dirty
srcmd5s. there is nothing we can do about it, but we can make sure
it's not become an error
[api] do not try to delete nothing

If a submit request is set to cleanup but is from home:$USER it won't
cleanup - but it shouldn't crash either
[api] refactor messages controller

I would like to get rid of it actually, it's never been used (in SUSE's
instances at least)
[api] refactor more of the source controller