Throw better exception when downloading gpg keys
Throw better exception when downloading gpg keys

As a result, the message that is raised to dnf is "Failed to synchronize cache
for repo..." and the original error is just logged as debug, instead of raising
the original error directly.

Conan-Kudo/libhif,rpm-software-management/libdnf,hughsie/libhif,hughsie/libhif,rpm-software-management/libhif,hughsie/libhif,hughsie/libhif,rpm-software-management/libhif,rpm-software-management/libdnf,Conan-Kudo/libhif,Conan-Kudo/libhif,rpm-software-management/libhif,rpm-software-management/libdnf,Conan-Kudo/libhif,rpm-software-management/libdnf,rpm-software-management/libhif