ARROW-3059: [C++] Remove namespace arrow::test

[pitrou]

Depends on PR apache/parquet-cpp#487

[codecov-io]

Codecov Report

Merging #2436 into master will increase coverage by 17.71%.
The diff coverage is 97.64%.

@@             Coverage Diff             @@
##           master    #2436       +/-   ##
===========================================
+ Coverage   69.01%   86.73%   +17.71%     
===========================================
  Files          61      239      +178     
  Lines        3234    42607    +39373     
===========================================
+ Hits         2232    36954    +34722     
- Misses        928     5653     +4725     
+ Partials       74        0       -74

Impacted Files	Coverage Δ
cpp/src/arrow/memory_pool-test.h	100% <ø> (ø)
cpp/src/arrow/io/io-hdfs-test.cc	17.44% <0%> (ø)
cpp/src/arrow/test-common.h	100% <100%> (ø)
cpp/src/arrow/util/compression-test.cc	100% <100%> (ø)
cpp/src/arrow/ipc/ipc-read-write-test.cc	99.04% <100%> (ø)
cpp/src/arrow/test-util.h	74.8% <100%> (ø)
cpp/src/arrow/util/lazy-test.cc	100% <100%> (ø)
cpp/src/arrow/memory_pool-test.cc	100% <100%> (ø)
cpp/src/arrow/compute/compute-test.cc	99.54% <100%> (ø)
cpp/src/arrow/array-test.cc	100% <100%> (ø)
... and 307 more

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[pitrou]

Hmm... I'm a bit surprised that CI succeeded without the required parquet-cpp changes.

[wesm]

Arrow's CI does not build the Parquet unit tests, which I presume are the only things affected by this

[pitrou]

Ah, I see, thanks.

[wesm]

+1. I will merge this and then we can bump the parquet-cpp Arrow version after we deal with PARQUET-1308