RFR: 8276306: jdk/jshell/CustomInputToolBuilder.java fails intermittently on storage acquisition

[Aleksey Shipilev]

This test intermittently fails in `tier1` runs on our highly parallel machines. I believe there is the interaction between the tests that use the preferences storage. See bug for the stack trace. I think we can fortify this test by overriding the default persistence storage.

Additional testing:
 - [x] 10x `langtools:tier1`, no failures now

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Commit messages:
 - Fix

Changes: https://git.openjdk.java.net/jdk/pull/6208/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=6208&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8276306
  Stats: 2 lines in 1 file changed: 2 ins; 0 del; 0 mod
  Patch: https://git.openjdk.java.net/jdk/pull/6208.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/6208/head:pull/6208

PR: https://git.openjdk.java.net/jdk/pull/6208