test_runner: simplify code and make it more consistent #1035

Job	Run time
Build slim tarball	1m 45s
aarch64-darwin: with shared libraries	33m 0s
aarch64-linux: with shared libraries	25m 1s
x86_64-linux: with shared libraries	28m 42s
x86_64-darwin: with shared libraries	46m 13s
	2h 14m 41s

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