Fix intermittent failure in fetchlimit test.

We were sending bursts of data with ditch.pl, if we then
use dig and hit the same port we will have a failure.
27 jobs for wpk-fetchlimit-intermittent-failure in 8 minutes and 15 seconds (queued for 2 seconds)
latest
Status Job ID Name Coverage
  Precheck
passed #83551
linux docker amd64
precheck:debian:sid:amd64

00:00:21

 
  Build
passed #83552
linux docker amd64
build:centos:centos6:amd64

00:02:45

passed #83553
linux docker amd64
build:centos:centos7:amd64

00:02:54

passed #83554
linux docker amd64
build:clang:debian:stretch:amd64

00:02:09

passed #83558
linux docker i386
build:clang:debian:stretch:i386

00:01:29

passed #83555
linux docker amd64
build:debian:jessie:amd64

00:02:03

passed #83557
linux docker amd64
build:debian:sid:amd64

00:02:08

passed #83559
linux docker i386
build:debian:sid:i386

00:01:34

passed #83556
linux docker amd64
build:debian:stretch:amd64

00:02:07

passed #83560
linux docker amd64
pkcs11:build:debian:sid:amd64

00:02:10

 
  Test
passed #83561
linux docker amd64
docs:debian:sid:amd64

00:00:51

passed #83575
linux docker amd64
install:debian:sid:amd64

00:01:51

passed #83577
linux docker amd64
pkcs11:systemtest:debian:sid:amd64

00:04:51

passed #83576
linux docker amd64
pkcs11:unittest:debian:sid:amd64

00:00:50

passed #83569
linux docker amd64
systemtest:centos:centos6:amd64

00:04:52

passed #83570
linux docker amd64
systemtest:centos:centos7:amd64

00:04:54

passed #83571
linux docker amd64
systemtest:debian:jessie:amd64

00:04:52

passed #83573
linux docker amd64
systemtest:debian:sid:amd64

00:04:54

passed #83574
linux docker i386
systemtest:debian:sid:i386

00:04:55

passed #83572
linux docker amd64
systemtest:debian:stretch:amd64

00:04:51

passed #83562
linux docker amd64
unittest:centos:centos6:amd64

00:00:57

passed #83563
linux docker amd64
unittest:centos:centos7:amd64

00:00:50

passed #83567
linux docker amd64
unittest:clang:debian:stretch:amd64

00:00:46

passed #83564
linux docker amd64
unittest:debian:jessie:amd64

00:00:58

passed #83566
linux docker amd64
unittest:debian:sid:amd64

00:00:50

passed #83568
linux docker i386
unittest:debian:sid:i386

00:00:46

passed #83565
linux docker amd64
unittest:debian:stretch:amd64

00:00:50