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_11 in 10 minutes and 5 seconds (queued for 5 seconds)
Status Job ID Name Coverage
  Precheck
passed #61431
amd64 docker linux
precheck:debian:sid:amd64

00:00:20

 
  Build
passed #61432
amd64 docker linux
build:centos:centos6:amd64

00:03:20

passed #61433
amd64 docker linux
build:centos:centos7:amd64

00:03:05

passed #61434
amd64 docker linux
build:debian:sid:amd64

00:02:01

passed #61435
i386 docker linux
build:debian:sid:i386

00:02:03

 
  Test
passed #61444
amd64 docker linux
install:debian:sid:amd64

00:03:25

passed #61440
amd64 docker linux
systemtest:centos:centos6:amd64

00:04:25

passed #61441
amd64 docker linux
systemtest:centos:centos7:amd64

00:04:36

passed #61442
amd64 docker linux
systemtest:debian:sid:amd64

00:04:20

passed #61443
i386 docker linux
systemtest:debian:sid:i386

00:04:45

passed #61436
amd64 docker linux
unittest:centos:centos6:amd64

00:01:10

passed #61437
amd64 docker linux
unittest:centos:centos7:amd64

00:01:11

passed #61438
amd64 docker linux
unittest:debian:sid:amd64

00:01:00

passed #61439
i386 docker linux
unittest:debian:sid:i386

00:00:57