speedup fetching rpmdb a bit by reusing what we can from the old cache.
speedup fetching rpmdb a bit by reusing what we can from the old cache.

Suggested by mls, thank you!

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