[MINOR] test: Use sensible partition ids in ShuffleReadClientImplTest

[EnricoMi]

What changes were proposed in this pull request?

Explicitly uses partition id 0 or 1 where sensible. Also adds a test that writes and reads two partitions.

Why are the changes needed?

In ShuffleReadClientImplTest, partition id 0 is implicitly used though some tests use HadoopShuffleWriteHandler with partition id 1, which is not realistic.

Does this PR introduce any user-facing change?

No.

How was this patch tested?

Unit tests.

[github-actions]

Test Results

2 312 files  ± 0  2 312 suites  ±0   4h 37m 23s ⏱️ + 1m 2s
  823 tests + 1    822 ✅ + 1   1 💤 ±0  0 ❌ ±0 
9 693 runs  +14  9 679 ✅ +14  14 💤 ±0  0 ❌ ±0 

Results for commit c720b10. ± Comparison against base commit a73dcb9.

♻️ This comment has been updated with latest results.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 54.57%. Comparing base (a73dcb9) to head (c720b10).

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #1545      +/-   ##
============================================
+ Coverage     53.62%   54.57%   +0.95%     
  Complexity     2816     2816              
============================================
  Files           436      416      -20     
  Lines         24536    22175    -2361     
  Branches       2076     2076              
============================================
- Hits          13157    12103    -1054     
+ Misses        10559     9322    -1237     
+ Partials        820      750      -70     

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[jerqi]

LGTM, thanks @EnricoMi