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ARROW-7863: [C++][Python][CI] Ensure running HDFS related tests

libhdfs3 backend may be broken. It causes SEGV. So libhdfs3 backend
test is disabled for now.

Closes #6432 from kou/cpp-hdfs-test-robust and squashes the following commits:

85b45ada8 <Sutou Kouhei> Remove libhdfs3 related code
b311877ca <Sutou Kouhei> Remove libhdfs3 support
b54664c7b <Sutou Kouhei>  Ensure running HDFS related tests

Authored-by: Sutou Kouhei <kou@clear-code.com>
Signed-off-by: Sutou Kouhei <kou@clear-code.com>