[api] fix removal of all _product:* package containers when _product gets deleted
refactor sync_to_stage

- also allow multiple stage servers and stage server partitioning
- also support a sync script
[api] avoid not reachable backend objects when package destroy throw an exception
[backend] support architecture specific update urls
[backend] support productdependency expansion for release packages
[backend] add test case with new style weak dependencies inside of rpm. rpmmd format must be still the same.
[dist] one more feature in 2.6
[api] follow changed srcmd5 of last test case submission
[webui] Don't pass status as Admin. Fixes issue #606