fix test_bucket_acl_grant_nonexist_user
fix test_bucket_acl_grant_nonexist_user

* Change user_id to avoid name conflict
* Check for error_code

andrewgaul/s3-tests,tobegit3hub/s3-tests,jmunhoz/s3-tests,robbat2/s3-tests,timuralp/s3-tests,Nexenta/s3-tests,basho/s3-tests,Nexenta/s3-tests,smithfarm/s3-tests,basho/s3-tests,timuralp/s3-tests,dreamhost/s3-tests,Nexenta/s3-tests,ceph/s3-tests,jmunhoz/s3-tests,robbat2/s3-tests,SUSE/s3-tests,piousbox/s3-tests,Intel-bigdata/s3-tests,Intel-bigdata/s3-tests,smithfarm/s3-tests,Nexenta/s3-tests,piousbox/s3-tests,dreamhost/s3-tests,andrewgaul/s3-tests,tobegit3hub/s3-tests,ceph/s3-tests,piousbox/s3-tests,SUSE/s3-tests