Make "kyua report-html" less verbose on stdout

"kyua report-html" command in CI generates more than two pages of output
to stdout, which is nothing but which HTML pages Kyua generated, e.g.:

  Generating kyua_html/context.html
  Generating kyua_html/lib_dns_tests_acl_test_main.html
  ...
  Generating kyua_html/lib_ns_tests_query_test_main.html
  Generating kyua_html/report.css
  Generating kyua_html/index.html

This is seldomly useful and requires the user to scroll three pages
upwards to get to unit test results.

(cherry picked from commit 74fa1962)
86 jobs for !4708 with mnowak/make-kyua-report-html-less-verbose-v9_11 in 59 seconds (queued for 12 seconds)
detached
Status Job ID Name Coverage
  Precheck
canceled #1506041
amd64 linux
autoreconf

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amd64 linux
clang-format

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amd64 linux
coccinelle

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amd64 linux
danger

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misc

 
  Build
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amd64 linux
clang:asan

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amd64 linux
clang:buster:amd64

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amd64 libvirt
clang:freebsd11:amd64

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amd64 libvirt
clang:freebsd12:amd64

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amd64 libvirt
clang:openbsd:amd64

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amd64 linux
clang:tsan

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amd64 linux
clang:tsan:noatomics

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gcc:alpine3.12:amd64

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amd64 linux
gcc:asan

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amd64 linux
gcc:buster:amd64

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amd64 linux
gcc:centos6:amd64

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i386 linux
gcc:centos6:i386

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amd64 linux
gcc:centos7:amd64

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amd64 linux
gcc:centos8:amd64

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amd64 linux
gcc:fedora33:amd64

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amd64 linux
gcc:focal:amd64

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amd64 linux
gcc:noatomics

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amd64 linux
gcc:out-of-tree

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amd64 linux
gcc:pkcs11

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gcc:sid:amd64

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amd64 linux
gcc:stretch:amd64

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amd64 linux
gcc:tsan:noatomics

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gcc:tumbleweed:amd64

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amd64 linux
gcc:xenial:amd64

passed #1506072
amd64 windows
msvc:windows:amd64

00:00:59

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nolibtool:sid:amd64

 
  Unit
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unit:clang:asan

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amd64 libvirt
unit:clang:freebsd12:amd64

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amd64 linux
unit:clang:tsan

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unit:clang:tsan:noatomics

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amd64 linux
unit:gcc:alpine3.12:amd64

canceled #1506085
amd64 linux
unit:gcc:asan

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amd64 linux
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amd64 linux
unit:gcc:centos6:amd64

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i386 linux
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amd64 linux
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amd64 linux
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amd64 linux
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amd64 linux
unit:gcc:focal:amd64

canceled #1506091
amd64 linux
unit:gcc:noatomics

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amd64 linux
unit:gcc:pkcs11

canceled #1506080
amd64 linux
unit:gcc:sid:amd64

canceled #1506078
amd64 linux
unit:gcc:stretch:amd64

canceled #1506087
amd64 linux
unit:gcc:tsan

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amd64 linux
unit:gcc:tsan:noatomics

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amd64 linux
unit:gcc:tumbleweed:amd64

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amd64 linux
unit:gcc:xenial:amd64

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  System
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system:clang:asan

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amd64 libvirt
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amd64 linux allowed to fail
system:clang:tsan

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amd64 linux allowed to fail
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amd64 linux
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amd64 linux
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amd64 linux
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amd64 linux
system:gcc:noatomics

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amd64 linux
system:gcc:pkcs11

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amd64 linux
system:gcc:sid:amd64

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amd64 linux
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canceled #1506111
amd64 linux allowed to fail
system:gcc:tsan

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amd64 linux allowed to fail
system:gcc:tsan:noatomics

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amd64 linux
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amd64 linux
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amd64 linux
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  Docs
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docs

 
  Postcheck
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cppcheck

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flake8

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gcov

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pylint

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