fix(tests/lean/interactive/test_single): do not use deprecated realpath command
fix(tests/lean/interactive/test_single): do not use deprecated realpath command

The realpath executable is not installed by default on ubuntu.  Also
contains a fix for macOS where the default readlink executable does not
understand -f.  The ./readlinkf.sh script does not work for directories
either.

fpvandoorn/lean,Kha/lean,johoelzl/lean,digama0/lean,avigad/lean,dselsam/lean,johoelzl/lean,leanprover-community/lean,fpvandoorn/lean,rlewis1988/lean,fgdorais/lean,dselsam/lean,fgdorais/lean,digama0/lean,avigad/lean,fgdorais/lean,digama0/lean,leodemoura/lean,digama0/lean,fgdorais/lean,rlewis1988/lean,dselsam/lean,rlewis1988/lean,leodemoura/lean,avigad/lean,Kha/lean,avigad/lean,fgdorais/lean,digama0/lean,Kha/lean,dselsam/lean,dselsam/lean,leanprover/lean,Kha/lean,leanprover-community/lean,leodemoura/lean,leanprover/lean,avigad/lean,fpvandoorn/lean,fgdorais/lean,fpvandoorn/lean,Kha/lean,digama0/lean,leanprover/lean,fpvandoorn/lean,johoelzl/lean,leanprover-community/lean,johoelzl/lean,Kha/lean,johoelzl/lean,leanprover-community/lean,leanprover/lean,leodemoura/lean,rlewis1988/lean,rlewis1988/lean,dselsam/lean,leanprover/lean,fpvandoorn/lean,leodemoura/lean,rlewis1988/lean,leanprover-community/lean,leodemoura/lean,leanprover/lean,leanprover-community/lean,avigad/lean,johoelzl/lean