Address test race condition in serve-stale

the dig.out.test# files could still be being written when the
content greps where being made.
74 jobs for !5143 with 2751-serve-stale-tests-false-negative in 19 minutes and 58 seconds (queued for 8 seconds)
latest detached
Status Job ID Name Coverage
  Autoconf
passed #1773501
amd64 linux
autoreconf

00:00:17

 
  Precheck
passed #1773503
amd64 linux
clang-format

00:00:19

passed #1773504
amd64 linux
coccinelle

00:04:30

passed #1773505
amd64 linux
danger

00:00:16

passed #1773502
amd64 linux
misc

00:00:18

passed #1773506
amd64 linux
tarball-create

00:01:28

 
  Build
passed #1773519
amd64 linux
clang:asan

00:02:06

passed #1773523
amd64 linux
clang:buster:amd64

00:01:03

passed #1773526
amd64 libvirt
clang:freebsd12:amd64

00:01:14

passed #1773527
amd64 libvirt
clang:freebsd13:amd64

00:03:03

passed #1773528
amd64 libvirt
clang:openbsd:amd64

00:02:10

passed #1773521
amd64 linux
clang:tsan

00:01:12

passed #1773507
amd64 linux
gcc:alpine3.13:amd64

00:00:57

passed #1773518
amd64 linux
gcc:asan

00:01:45

passed #1773516
amd64 linux
gcc:bionic:amd64

00:01:01

passed #1773511
amd64 linux
gcc:buster:amd64

00:00:46

passed #1773508
amd64 linux
gcc:centos7:amd64

00:00:56

passed #1773509
amd64 linux
gcc:centos8:amd64

00:00:54

passed #1773517
amd64 linux
gcc:focal:amd64

00:00:57

passed #1773522
amd64 linux
gcc:mutexatomics

00:00:53

passed #1773513
amd64 linux
gcc:out-of-tree

00:00:51

passed #1773512
amd64 linux
gcc:sid:amd64

00:01:06

passed #1773524
amd64 linux
gcc:softhsm2.4

00:00:59

passed #1773525
amd64 linux
gcc:softhsm2.6

00:00:55

passed #1773510
amd64 linux
gcc:stretch:amd64

00:01:05

passed #1773514
amd64 linux
gcc:tarball

00:01:23

passed #1773520
amd64 linux
gcc:tsan

00:01:10

passed #1773515
amd64 linux
gcc:tumbleweed:amd64

00:00:57

passed #1773529
amd64 windows
msvc:windows:amd64

00:00:49

 
  Unit
passed #1773540
amd64 linux
unit:clang:asan

00:02:17

passed #1773544
amd64 linux
unit:clang:buster:amd64

00:01:27

passed #1773547
amd64 libvirt
unit:clang:freebsd12:amd64

00:01:43

passed #1773548
amd64 libvirt
unit:clang:freebsd13:amd64

00:03:33

passed #1773549
amd64 libvirt
unit:clang:openbsd:amd64

00:03:22

passed #1773542
amd64 linux
unit:clang:tsan

00:03:35

passed #1773530
amd64 linux
unit:gcc:alpine3.13:amd64

00:01:38

passed #1773539
amd64 linux
unit:gcc:asan

00:02:14

passed #1773537
amd64 linux
unit:gcc:bionic:amd64

00:01:21

passed #1773534
amd64 linux
unit:gcc:buster:amd64

00:02:34

passed #1773531
amd64 linux
unit:gcc:centos7:amd64

00:01:27

passed #1773532
amd64 linux
unit:gcc:centos8:amd64

00:01:30

passed #1773538
amd64 linux
unit:gcc:focal:amd64

00:01:27

passed #1773543
amd64 linux
unit:gcc:mutexatomics

00:01:35

passed #1773535
amd64 linux
unit:gcc:sid:amd64

00:01:31

passed #1773545
amd64 linux
unit:gcc:softhsm2.4

00:01:27

passed #1773546
amd64 linux
unit:gcc:softhsm2.6

00:01:24

passed #1773533
amd64 linux
unit:gcc:stretch:amd64

00:00:14

passed #1773541
amd64 linux
unit:gcc:tsan

00:04:22

passed #1773536
amd64 linux
unit:gcc:tumbleweed:amd64

00:01:25

 
  System
passed #1773560
amd64 linux
system:clang:asan

00:14:34

passed #1773564
amd64 linux
system:clang:buster:amd64

00:12:25

passed #1773567
amd64 libvirt
system:clang:freebsd12:amd64

00:11:51

passed #1773568
amd64 libvirt
system:clang:freebsd13:amd64

00:13:24

passed #1773562
amd64 linux
system:clang:tsan

00:16:33

passed #1773550
amd64 linux
system:gcc:alpine3.13:amd64

00:12:51

passed #1773559
amd64 linux
system:gcc:asan

00:15:11

passed #1773557
amd64 linux
system:gcc:bionic:amd64

00:11:27

passed #1773554
amd64 linux
system:gcc:buster:amd64

00:13:54

passed #1773551
amd64 linux
system:gcc:centos7:amd64

00:12:02

passed #1773552
amd64 linux
system:gcc:centos8:amd64

00:12:08

passed #1773558
amd64 linux
system:gcc:focal:amd64

00:12:35

passed #1773563
amd64 linux
system:gcc:mutexatomics

00:12:34

passed #1773555
amd64 linux
system:gcc:sid:amd64

00:12:31

passed #1773565
amd64 linux
system:gcc:softhsm2.4

00:12:43

passed #1773566
amd64 linux
system:gcc:softhsm2.6

00:12:04

passed #1773553
amd64 linux
system:gcc:stretch:amd64

00:11:54

passed #1773561
amd64 linux
system:gcc:tsan

00:16:51

passed #1773556
amd64 linux
system:gcc:tumbleweed:amd64

00:11:51

 
  Docs
passed #1773569
amd64 linux
docs

00:00:50

 
  Postcheck
passed #1773573
amd64 linux
cppcheck

00:00:43

passed #1773570
amd64 linux
flake8

00:00:20

passed #1773574
amd64 linux
gcov

00:00:33

78.0%
passed #1773571
amd64 linux
pylint

00:00:49

passed #1773572
amd64 linux
scan-build

00:04:08