t/t1304: use 'test -r' to test readability rather than looking at mode bits

t/t1304: use 'test -r' to test readability rather than looking at mode bits

This test was using the group read permission bit as an indicator of the
default ACL mask.  This behavior is valid on Linux but not on other
platforms like Solaris.  So, rather than looking at mode bits, just test
readability for the user.  This, along with the checks for the existence
of the ACL's that were set on the parent directories, should be enough.

Signed-off-by: Brandon Casey <casey@nrlssc.navy.mil>
Signed-off-by: Junio C Hamano <gitster@pobox.com>