quota: fix backward compatibility of quota xattr version

quota: fix backward compatibility of quota xattr version

quota-version features is implemented for 3.7.6
please see below patch for more details:
http://review.gluster.org/#/c/12386

Problem is when quota is already enabled,
we suffix 0 to contri xattr key. for backward compatibility
don't add suffix if quota-version is 0

Change-Id: Id7d713b18d989e4e86019969eb511617848127f2
BUG: 1283567
Signed-off-by: vmallika <vmallika@redhat.com>
Reviewed-on: http://review.gluster.org/12660
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Tested-by: NetBSD Build System <jenkins@build.gluster.org>
Reviewed-by: Raghavendra G <rgowdapp@redhat.com>