tests: make dd less noisy

Also fixed one case in quota.t where error output is expected.  There
are probably other similar cases which can be fixed separately.

Change-Id: If80fad0d9fcff6f8ca91d00f4f7b2d5f3fef4256
Signed-off-by: Jeff Darcy <jdarcy@redhat.com>
Reviewed-on: http://review.gluster.org/8298
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Humble Devassy Chirammal <humble.devassy@gmail.com>
Reviewed-by: Prashanth Pai <ppai@redhat.com>
Reviewed-by: Vijay Bellur <vbellur@redhat.com>