Associate unit test data dir with a more specific variable

Having 'TESTS', the Automake variable and 'TESTS' the unit test data dir
seems confusing, lets rename the latter to to 'TESTS_DIR'.
82 jobs for !3656 with 1726-unit-tests-rename-tests-to-something-more-descriptive-v9_11 in 2 minutes and 31 seconds (queued for 9 seconds)
detached
Status Job ID Name Coverage
  Precheck
canceled #931962
amd64 linux
autoreconf

canceled #931964
amd64 linux
clang-format

canceled #931965
amd64 linux
coccinelle

canceled #931966
amd64 linux
danger

canceled #931963
amd64 linux
misc

 
  Build
canceled #931982
amd64 linux
clang:asan

canceled #931986
amd64 linux
clang:buster:amd64

canceled #931988
amd64 libvirt
clang:freebsd11.3:amd64

canceled #931989
amd64 libvirt
clang:freebsd12.1:amd64

canceled #931990
amd64 libvirt
clang:openbsd6.6:amd64

canceled #931984
amd64 linux
clang:tsan

canceled #931967
amd64 linux
gcc:alpine3.11:amd64

canceled #931981
amd64 linux
gcc:asan

canceled #931980
amd64 linux
gcc:bionic:amd64

canceled #931972
amd64 linux
gcc:buster:amd64

canceled #931968
amd64 linux
gcc:centos6:amd64

canceled #931969
amd64 linux
gcc:centos7:amd64

canceled #931970
amd64 linux
gcc:centos8:amd64

canceled #931978
amd64 linux
gcc:fedora31:amd64

canceled #931985
amd64 linux
gcc:mutexatomics

canceled #931974
amd64 linux
gcc:out-of-tree

canceled #931987
amd64 linux
gcc:pkcs11

canceled #931973
amd64 linux
gcc:sid:amd64

canceled #931975
arm64 linux
gcc:sid:arm64

canceled #931976
i386 linux
gcc:sid:i386

canceled #931971
amd64 linux
gcc:stretch:amd64

canceled #931983
amd64 linux
gcc:tsan

canceled #931977
amd64 linux
gcc:tumbleweed:amd64

canceled #931979
amd64 linux
gcc:xenial:amd64

passed #931992
amd64 windows
msvc:windows:amd64

00:02:31

canceled #931991
amd64 linux
nolibtool:sid:amd64

 
  Unit
canceled #932007
amd64 linux
unit:clang:asan

canceled #932011
amd64 linux
unit:clang:buster:amd64

canceled #932013
amd64 libvirt
unit:clang:freebsd11.3:amd64

canceled #932014
amd64 libvirt
unit:clang:freebsd12.1:amd64

canceled #932009
amd64 linux allowed to fail
unit:clang:tsan

canceled #931993
amd64 linux
unit:gcc:alpine3.11:amd64

canceled #932006
amd64 linux
unit:gcc:asan

canceled #932005
amd64 linux
unit:gcc:bionic:amd64

canceled #931998
amd64 linux
unit:gcc:buster:amd64

canceled #931994
amd64 linux
unit:gcc:centos6:amd64

canceled #931995
amd64 linux
unit:gcc:centos7:amd64

canceled #931996
amd64 linux
unit:gcc:centos8:amd64

canceled #932003
amd64 linux
unit:gcc:fedora31:amd64

canceled #932010
amd64 linux
unit:gcc:mutexatomics

canceled #932012
amd64 linux
unit:gcc:pkcs11

canceled #931999
amd64 linux
unit:gcc:sid:amd64

canceled #932000
arm64 linux
unit:gcc:sid:arm64

canceled #932001
i386 linux
unit:gcc:sid:i386

canceled #931997
amd64 linux
unit:gcc:stretch:amd64

canceled #932008
amd64 linux allowed to fail
unit:gcc:tsan

canceled #932002
amd64 linux
unit:gcc:tumbleweed:amd64

canceled #932004
amd64 linux
unit:gcc:xenial:amd64

canceled #932015
amd64 linux
unit:nolibtool:sid:amd64

 
  System
canceled #932030
amd64 linux
system:clang:asan

canceled #932034
amd64 linux
system:clang:buster:amd64

canceled #932036
amd64 libvirt
system:clang:freebsd11.3:amd64

canceled #932037
amd64 libvirt
system:clang:freebsd12.1:amd64

canceled #932032
amd64 linux allowed to fail
system:clang:tsan

canceled #932016
amd64 linux
system:gcc:alpine3.11:amd64

canceled #932029
amd64 linux
system:gcc:asan

canceled #932028
amd64 linux
system:gcc:bionic:amd64

canceled #932021
amd64 linux
system:gcc:buster:amd64

canceled #932017
amd64 linux
system:gcc:centos6:amd64

canceled #932018
amd64 linux
system:gcc:centos7:amd64

canceled #932019
amd64 linux
system:gcc:centos8:amd64

canceled #932026
amd64 linux
system:gcc:fedora31:amd64

canceled #932033
amd64 linux
system:gcc:mutexatomics

canceled #932035
amd64 linux
system:gcc:pkcs11

canceled #932022
amd64 linux
system:gcc:sid:amd64

canceled #932023
arm64 linux
system:gcc:sid:arm64

canceled #932024
i386 linux
system:gcc:sid:i386

canceled #932020
amd64 linux
system:gcc:stretch:amd64

canceled #932031
amd64 linux allowed to fail
system:gcc:tsan

canceled #932025
amd64 linux
system:gcc:tumbleweed:amd64

canceled #932027
amd64 linux
system:gcc:xenial:amd64

canceled #932038
amd64 linux
system:nolibtool:sid:amd64

 
  Docs
canceled #932039
amd64 linux
docs

 
  Postcheck
canceled #932043
amd64 linux
cppcheck

canceled #932040
amd64 linux
flake8

canceled #932041
amd64 linux
pylint

canceled #932042
amd64 linux
scan-build