Librepo API changes

Librepo now raises IOError instead of LibrepoException for:
LRE_IO, LRE_CANNOTCREATEDIR, LRE_CANNOTCREATETMP
repo: use all mirrors/baseurls when downloading a package.

dep: this is only allowed by the 0fbe1c3 commit in librepo.

Related: RhBug:997658