zero: send grep output to /dev/null; set ret=0 at start of 'check repeated...

zero: send grep output to /dev/null; set ret=0 at start of 'check repeated recursive lookups of non recurring TTL=0 responses get new values' test so the failed subtest count is correct

(cherry picked from commit a6507af9)
14 jobs for 569-zero-system-test-failed-to-set-ret-0-and-send-output-to-dev-null-v9_12 in 9 minutes and 13 seconds (queued for 6 seconds)
Status Job ID Name Coverage
  Precheck
passed #61417
amd64 docker linux
precheck:debian:sid:amd64

00:00:18

 
  Build
passed #61418
amd64 docker linux
build:centos:centos6:amd64

00:02:35

passed #61419
amd64 docker linux
build:centos:centos7:amd64

00:02:43

passed #61420
amd64 docker linux
build:debian:sid:amd64

00:01:52

passed #61421
i386 docker linux
build:debian:sid:i386

00:02:01

 
  Test
passed #61430
amd64 docker linux
install:debian:sid:amd64

00:03:48

passed #61426
amd64 docker linux
systemtest:centos:centos6:amd64

00:05:01

passed #61427
amd64 docker linux
systemtest:centos:centos7:amd64

00:05:06

passed #61428
amd64 docker linux
systemtest:debian:sid:amd64

00:05:24

passed #61429
i386 docker linux
systemtest:debian:sid:i386

00:05:27

passed #61422
amd64 docker linux
unittest:centos:centos6:amd64

00:01:01

passed #61423
amd64 docker linux
unittest:centos:centos7:amd64

00:00:57

passed #61424
amd64 docker linux
unittest:debian:sid:amd64

00:00:56

passed #61425
i386 docker linux
unittest:debian:sid:i386

00:00:57