ARROW-2575: [Python] Exclude hidden files starting with . in ParquetManifest

[wesm]

I also moved a large nested helper function to a slightly more appropriate place (we need to develop abstract interfaces for different partition schemes)

[codecov-io]

Codecov Report

Merging #2312 into master will increase coverage by 2.39%.
The diff coverage is 96.42%.

@@            Coverage Diff             @@
##           master    #2312      +/-   ##
==========================================
+ Coverage   84.38%   86.77%   +2.39%     
==========================================
  Files         293      237      -56     
  Lines       44784    42056    -2728     
==========================================
- Hits        37789    36494    -1295     
+ Misses       6964     5562    -1402     
+ Partials       31        0      -31

Impacted Files	Coverage Δ
python/pyarrow/tests/test_parquet.py	97.02% <100%> (+0.03%)	⬆️
python/pyarrow/parquet.py	91.1% <94.28%> (+0.01%)	⬆️
go/arrow/math/int64_amd64.go
go/arrow/internal/testing/tools/bits.go
go/arrow/math/float64_sse4_amd64.go
go/arrow/memory/buffer.go
go/arrow/math/int64_avx2_amd64.go
go/arrow/math/float64_avx2_amd64.go
go/arrow/memory/memory_sse4_amd64.go
rust/src/buffer.rs
... and 49 more

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[xhochy]

+1, LGTM