add fails_on_dho on a failing test

It turns out that the e-mail comments were legitimate. The reason the
tests were passing was because the specific users now had e-mail
addresses, but this not the default case.

s3tests/functional/test_s3.py

@@ -1614,6 +1614,10 @@ def test_bucket_acl_no_grants():
     bucket.set_acl('private')
 
 
+# This test will fail on DH Objects. DHO allows multiple users with one account, which
+# would violate the uniqueness requirement of a user's email. As such, DHO users are
+# created without an email.
+@attr('fails_on_dho')
 def test_bucket_acl_grant_email():
     bucket = get_new_bucket()
     # add alt user