Cannot resolve builds done in side tags

[msimacek]

Koschei cannot resolve builds that were done in tag different from build tags we know. The reason is that it needs to know which arches to use for given tag.

[mizdebsk]

This has been a known problem for a long time. It also happens at branching time, eg. when rawhide moves from f24 to f25 - Koschei is unable to resolve older builds that were still done in f24-build repo.

[msimacek]

I think, the only thing preventing it from resolving them is that it doesn't know which arches to use. We need two pieces of information - which arches to download repos from and which arch to use as resolution arch. We can probably have resolution arch specified in the config globally. For repo arches, we can get those with getTag from Koji, but it also lists arches which we don't want to download for performance resons (arm). So maybe we could use getTag and have global arch whitelist in the configuration?