Regression test portability: quota.t

- Use du -k to have size reported in kB, as NetBSD defaults to blocks
- on overquota, Linux says 'No space left' and NetBSD 'Disc quota exceeded'

BUG: 1129939
Change-Id: I6a2baef94cb60e9fabf06a6f8d01f2acb6ee0a30
Signed-off-by: Emmanuel Dreyfus <manu@netbsd.org>
Reviewed-on: http://review.gluster.org/8930
Reviewed-by: Jeff Darcy <jdarcy@redhat.com>
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Vijay Bellur <vbellur@redhat.com>