Use buffered reads when recovering coverage result.

[y-higuchi]

Use buffered reads when recovering coverage result.

After we started using this plugin,
we noticed fairly large number of 1 byte reads hitting NFS server hurting performance.

1 byte reads seems to be coming from PeekInputStream calls used inside ObjectInputStream
directly hitting FileInputStream.

This PR attempts to mitigate the issue by inserting BufferedInputStream to reduce number of small size reads
directly hitting the file system.

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[codecov]

Codecov Report

Merging #609 (17e3042) into master (38966f3) will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##             master     #609   +/-   ##
=========================================
  Coverage     72.30%   72.30%           
  Complexity     1573     1573           
=========================================
  Files           127      127           
  Lines          6067     6067           
  Branches        636      636           
=========================================
  Hits           4387     4387           
  Misses         1460     1460           
  Partials        220      220           

Impacted Files	Coverage Δ
...io/jenkins/plugins/coverage/CoverageProcessor.java	83.55% <100.00%> (ø)

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[uhafner]

Thanks for your PR.

Please note that this code actually is part of the deprecated code base. This code is not used when you use the new coverage step recordCoverage.