py: more detailed error string in Sack.add_cmdline_package().
py: more detailed error string in Sack.add_cmdline_package().

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