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).
77 jobs for !4313 with michal/enable-stress-tests-to-be-run-on-demand in 58 seconds (queued for 8 seconds)
detached
Status Job ID Name Coverage
  Autoconf
passed #1311831
amd64 linux
autoreconf

00:00:17

 
  Precheck
passed #1311833
amd64 linux
clang-format

00:00:18

canceled #1311834
amd64 linux
coccinelle

00:00:41

passed #1311907
linux amd64
danger

00:00:15

passed #1311832
amd64 linux
misc

00:00:21

canceled #1311836
amd64 linux
tarball-create

00:00:23

failed #1311835
amd64 linux
danger

00:00:14

 
  Build
canceled #1311849
amd64 linux
clang:asan

canceled #1311853
amd64 linux
clang:buster:amd64

canceled #1311856
amd64 libvirt
clang:freebsd11:amd64

00:00:22

canceled #1311857
amd64 libvirt
clang:freebsd12:amd64

canceled #1311858
amd64 libvirt
clang:openbsd:amd64

canceled #1311851
amd64 linux
clang:tsan

canceled #1311837
amd64 linux
gcc:alpine3.12:amd64

canceled #1311848
amd64 linux
gcc:asan

canceled #1311841
amd64 linux
gcc:buster:amd64

00:00:21

canceled #1311838
amd64 linux
gcc:centos7:amd64

00:00:23

canceled #1311839
amd64 linux
gcc:centos8:amd64

00:00:22

canceled #1311847
amd64 linux
gcc:focal:amd64

canceled #1311852
amd64 linux
gcc:mutexatomics

canceled #1311843
amd64 linux
gcc:out-of-tree

00:00:20

canceled #1311842
amd64 linux
gcc:sid:amd64

00:00:20

canceled #1311844
i386 linux
gcc:sid:i386

00:00:20

canceled #1311854
amd64 linux
gcc:softhsm2.4

canceled #1311855
amd64 linux
gcc:softhsm2.6

canceled #1311840
amd64 linux
gcc:stretch:amd64

00:00:21

canceled #1311850
amd64 linux
gcc:tsan

canceled #1311845
amd64 linux
gcc:tumbleweed:amd64

00:00:18

canceled #1311846
amd64 linux
gcc:xenial:amd64

canceled #1311859
amd64 windows
msvc:windows:amd64

00:00:40

 
  Unit
canceled #1311871
amd64 linux
unit:clang:asan

canceled #1311875
amd64 linux
unit:clang:buster:amd64

canceled #1311878
amd64 libvirt
unit:clang:freebsd11:amd64

canceled #1311879
amd64 libvirt
unit:clang:freebsd12:amd64

canceled #1311880
amd64 libvirt
unit:clang:openbsd:amd64

canceled #1311873
amd64 linux
unit:clang:tsan

canceled #1311860
amd64 linux
unit:gcc:alpine3.12:amd64

canceled #1311870
amd64 linux
unit:gcc:asan

canceled #1311864
amd64 linux
unit:gcc:buster:amd64

canceled #1311861
amd64 linux
unit:gcc:centos7:amd64

canceled #1311862
amd64 linux
unit:gcc:centos8:amd64

canceled #1311869
amd64 linux
unit:gcc:focal:amd64

canceled #1311874
amd64 linux
unit:gcc:mutexatomics

canceled #1311865
amd64 linux
unit:gcc:sid:amd64

canceled #1311866
i386 linux
unit:gcc:sid:i386

canceled #1311876
amd64 linux
unit:gcc:softhsm2.4

canceled #1311877
amd64 linux
unit:gcc:softhsm2.6

canceled #1311863
amd64 linux
unit:gcc:stretch:amd64

canceled #1311872
amd64 linux
unit:gcc:tsan

canceled #1311867
amd64 linux
unit:gcc:tumbleweed:amd64

canceled #1311868
amd64 linux
unit:gcc:xenial:amd64

 
  System
canceled #1311892
amd64 linux
system:clang:asan

canceled #1311896
amd64 linux
system:clang:buster:amd64

canceled #1311899
amd64 libvirt
system:clang:freebsd11:amd64

canceled #1311900
amd64 libvirt
system:clang:freebsd12:amd64

canceled #1311894
amd64 linux allowed to fail
system:clang:tsan

canceled #1311881
amd64 linux
system:gcc:alpine3.12:amd64

canceled #1311891
amd64 linux
system:gcc:asan

canceled #1311885
amd64 linux
system:gcc:buster:amd64

canceled #1311882
amd64 linux
system:gcc:centos7:amd64

canceled #1311883
amd64 linux
system:gcc:centos8:amd64

canceled #1311890
amd64 linux
system:gcc:focal:amd64

canceled #1311895
amd64 linux
system:gcc:mutexatomics

canceled #1311886
amd64 linux
system:gcc:sid:amd64

canceled #1311887
i386 linux
system:gcc:sid:i386

canceled #1311897
amd64 linux
system:gcc:softhsm2.4

canceled #1311898
amd64 linux
system:gcc:softhsm2.6

canceled #1311884
amd64 linux
system:gcc:stretch:amd64

canceled #1311893
amd64 linux allowed to fail
system:gcc:tsan

canceled #1311888
amd64 linux
system:gcc:tumbleweed:amd64

canceled #1311889
amd64 linux
system:gcc:xenial:amd64

 
  Docs
canceled #1311901
amd64 linux
docs

 
  Postcheck
canceled #1311905
amd64 linux
cppcheck

canceled #1311902
amd64 linux
flake8

canceled #1311906
amd64 linux
gcov

canceled #1311903
amd64 linux
pylint

canceled #1311904
amd64 linux
scan-build