Regression test portability: dd

Use dd msgfmt=quiet also in truncate replacement

BUG: 764655
Change-Id: I5ad022c1dc65ecc98996ccbe8a3d0e9de162aa1a
Signed-off-by: Emmanuel Dreyfus <manu@netbsd.org>
Reviewed-on: http://review.gluster.org/8464
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Harshavardhana <harsha@harshavardhana.net>
Tested-by: Harshavardhana <harsha@harshavardhana.net>