RFR: 7902831: Provide way to isolate tests from general concurrency

[Igor Ignatyev]

a prototype solution of [CODETOOLS-7902831](https://bugs.openjdk.java.net/browse/CODETOOLS-7902831) which changes `exclusiveAccess` tests to behave "nonconcurrent" one and uses read-write lock.

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Commit messages:
 - use read-write lock

Changes: https://git.openjdk.java.net/jtreg/pull/4/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jtreg&pr=4&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-7902831
  Stats: 65 lines in 4 files changed: 37 ins; 12 del; 16 mod
  Patch: https://git.openjdk.java.net/jtreg/pull/4.diff
  Fetch: git fetch https://git.openjdk.java.net/jtreg pull/4/head:pull/4

PR: https://git.openjdk.java.net/jtreg/pull/4