tests: rename some with more descriptive names * t/tar3.sh: Rename ... * t/tar-opts-errors.sh: ... like this. * t/tar2.sh: Rename... * t/tar-pax.sh: ... like this. * t/tar.sh: Rename ... * t/tar-ustar.sh: ... like this. * t/list-of-tests.mk: Adjust. Signed-off-by: Stefano Lattarini <stefano.lattarini@gmail.com>