t1301: don't fail in case setfacl(1) doesn't exist or fails

t1301: don't fail in case setfacl(1) doesn't exist or fails

In t1301 we're trying to remove any potentially-existing default ACLs
that might exist on the transh directory by executing setfacl(1).
According to 8ed0a740dd (t1301-shared-repo.sh: don't let a default ACL
interfere with the test, 2008-10-16), this is done because we play
around with permissions and umasks in this test suite.

The setfacl(1) binary may not exist on some systems though, even though
tests ultimately still pass. This doesn't matter currently, but will
cause the test to fail once we start running with `set -e`. Silence such
failures by ignoring failures here.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>