Enable "stress" tests to be run on demand

The "stress" test can be run in different ways, depending on:

  - the tested scenario (authoritative, recursive),
  - the operating system used (Linux, FreeBSD),
  - the architecture used (amd64, arm64).

Currently, all supported "stress" test variants are automatically
launched for all scheduled pipelines and for pipelines started for tags;
there is no possibility of running these tests on demand, which could be
useful in certain circumstances.

Employ the "only:variables" key to enable fine-grained control over the
list of "stress" test jobs to be run for a given pipeline.  Three CI
variables are used to specify the list of "stress" test jobs to create:

  - BIND_STRESS_TEST_MODE: specifies the test mode to use; must be
    explicitly set in order for any "stress" test job to be created;
    allowed values are: "authoritative", "recursive",

  - BIND_STRESS_TEST_OS: specifies the operating system to run the test
    on; allowed values are: "linux", "freebsd"; defaults to "linux", may
    be overridden at pipeline creation time,

  - BIND_STRESS_TEST_ARCH: specifies the architecture to run the test
    on; allowed values are: "amd64", "arm64"; defaults to "amd64", may
    be overridden at pipeline creation time.

Since case-insensitive regular expressions are used for determining
which jobs to run, every variable described above may contain multiple
values.  For example, setting the BIND_STRESS_TEST_MODE variable to
"authoritative,recursive" will cause the "stress" test to be run in both
supported scenarios (either on the default OS/architecture combination,
i.e. Linux/amd64, or, if the relevant variables are explicitly
specified, the requested OS/architecture combinations).
76 jobs for !4313 with michal/enable-stress-tests-to-be-run-on-demand in 34 seconds (queued for 12 seconds)
detached
Status Job ID Name Coverage
  Autoconf
canceled #1252032
amd64 linux
autoreconf

 
  Precheck
canceled #1252034
amd64 linux
clang-format

canceled #1252035
amd64 linux
coccinelle

canceled #1252036
amd64 linux
danger

canceled #1252033
amd64 linux
misc

canceled #1252037
amd64 linux
tarball-create

 
  Build
canceled #1252050
amd64 linux
clang:asan

canceled #1252054
amd64 linux
clang:buster:amd64

canceled #1252057
amd64 libvirt
clang:freebsd11:amd64

canceled #1252058
amd64 libvirt
clang:freebsd12:amd64

canceled #1252059
amd64 libvirt
clang:openbsd:amd64

canceled #1252052
amd64 linux
clang:tsan

canceled #1252038
amd64 linux
gcc:alpine3.12:amd64

canceled #1252049
amd64 linux
gcc:asan

canceled #1252042
amd64 linux
gcc:buster:amd64

canceled #1252039
amd64 linux
gcc:centos7:amd64

canceled #1252040
amd64 linux
gcc:centos8:amd64

canceled #1252048
amd64 linux
gcc:focal:amd64

canceled #1252053
amd64 linux
gcc:mutexatomics

canceled #1252044
amd64 linux
gcc:out-of-tree

canceled #1252043
amd64 linux
gcc:sid:amd64

canceled #1252045
i386 linux
gcc:sid:i386

canceled #1252055
amd64 linux
gcc:softhsm2.4

canceled #1252056
amd64 linux
gcc:softhsm2.6

canceled #1252041
amd64 linux
gcc:stretch:amd64

canceled #1252051
amd64 linux
gcc:tsan

canceled #1252046
amd64 linux
gcc:tumbleweed:amd64

canceled #1252047
amd64 linux
gcc:xenial:amd64

canceled #1252060
amd64 windows
msvc:windows:amd64

00:00:34

 
  Unit
canceled #1252072
amd64 linux
unit:clang:asan

canceled #1252076
amd64 linux
unit:clang:buster:amd64

canceled #1252079
amd64 libvirt
unit:clang:freebsd11:amd64

canceled #1252080
amd64 libvirt
unit:clang:freebsd12:amd64

canceled #1252081
amd64 libvirt
unit:clang:openbsd:amd64

canceled #1252074
amd64 linux
unit:clang:tsan

canceled #1252061
amd64 linux
unit:gcc:alpine3.12:amd64

canceled #1252071
amd64 linux
unit:gcc:asan

canceled #1252065
amd64 linux
unit:gcc:buster:amd64

canceled #1252062
amd64 linux
unit:gcc:centos7:amd64

canceled #1252063
amd64 linux
unit:gcc:centos8:amd64

canceled #1252070
amd64 linux
unit:gcc:focal:amd64

canceled #1252075
amd64 linux
unit:gcc:mutexatomics

canceled #1252066
amd64 linux
unit:gcc:sid:amd64

canceled #1252067
i386 linux
unit:gcc:sid:i386

canceled #1252077
amd64 linux
unit:gcc:softhsm2.4

canceled #1252078
amd64 linux
unit:gcc:softhsm2.6

canceled #1252064
amd64 linux
unit:gcc:stretch:amd64

canceled #1252073
amd64 linux
unit:gcc:tsan

canceled #1252068
amd64 linux
unit:gcc:tumbleweed:amd64

canceled #1252069
amd64 linux
unit:gcc:xenial:amd64

 
  System
canceled #1252093
amd64 linux
system:clang:asan

canceled #1252097
amd64 linux
system:clang:buster:amd64

canceled #1252100
amd64 libvirt
system:clang:freebsd11:amd64

canceled #1252101
amd64 libvirt
system:clang:freebsd12:amd64

canceled #1252095
amd64 linux allowed to fail
system:clang:tsan

canceled #1252082
amd64 linux
system:gcc:alpine3.12:amd64

canceled #1252092
amd64 linux
system:gcc:asan

canceled #1252086
amd64 linux
system:gcc:buster:amd64

canceled #1252083
amd64 linux
system:gcc:centos7:amd64

canceled #1252084
amd64 linux
system:gcc:centos8:amd64

canceled #1252091
amd64 linux
system:gcc:focal:amd64

canceled #1252096
amd64 linux
system:gcc:mutexatomics

canceled #1252087
amd64 linux
system:gcc:sid:amd64

canceled #1252088
i386 linux
system:gcc:sid:i386

canceled #1252098
amd64 linux
system:gcc:softhsm2.4

canceled #1252099
amd64 linux
system:gcc:softhsm2.6

canceled #1252085
amd64 linux
system:gcc:stretch:amd64

canceled #1252094
amd64 linux allowed to fail
system:gcc:tsan

canceled #1252089
amd64 linux
system:gcc:tumbleweed:amd64

canceled #1252090
amd64 linux
system:gcc:xenial:amd64

 
  Docs
canceled #1252102
amd64 linux
docs

 
  Postcheck
canceled #1252106
amd64 linux
cppcheck

canceled #1252103
amd64 linux
flake8

canceled #1252107
amd64 linux
gcov

canceled #1252104
amd64 linux
pylint

canceled #1252105
amd64 linux
scan-build