Regression test portability: mktemp

Linux mktemp accepts to run without a template, NetBSD mandates it. Since
the template option has the same syntax, add it everywhere. While there,
also do this in scripts outside of regression testing.

BUG: 764655
Change-Id: I3ec140afbc9009257c81a56d77afcc21fef74cc4
Signed-off-by: Emmanuel Dreyfus <manu@netbsd.org>
Reviewed-on: http://review.gluster.org/8432
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Harshavardhana <harsha@harshavardhana.net>
Tested-by: Harshavardhana <harsha@harshavardhana.net>