RFR: 8273961: [testbug] jdk/nio/zipfs/ZipFSTester.java fails if the path has plus character

[Remilia Scarlet]

Add the pre-processing to replace "+" by "%2b" which avoids `URLDecoder.decoder` changing the path unexpectedly.

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Commit messages:
 - 8273961: [testbug] jdk/nio/zipfs/ZipFSTester.java fails if the path has plus character

Changes: https://git.openjdk.java.net/jdk/pull/5574/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=5574&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8273961
  Stats: 4 lines in 1 file changed: 1 ins; 0 del; 3 mod
  Patch: https://git.openjdk.java.net/jdk/pull/5574.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/5574/head:pull/5574

PR: https://git.openjdk.java.net/jdk/pull/5574