[jdk11u-dev] RFR: 8225471: Test utility jdk.test.lib.util.FileUtils.areAllMountPointsAccessible needs to tolerate duplicates

[Amos Shi]

Backport of [JDK-8225471](https://bugs.openjdk.org/browse/JDK-8225471)

Note. The diff for file `test/jdk/java/nio/file/FileStore/Basic.java` cannot be applied automatically
- Because the `Copyright (c) year` section in Current code base is newer (`2020` vs `2022`)
- So this year line change has been ignored
- The change to this file can be considered `clear`

-------------

Commit messages:
 - Backport f4f7dbd54cf9d309039122e46ab8577bc3fd950a

Changes: https://git.openjdk.org/jdk11u-dev/pull/2332/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk11u-dev&pr=2332&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8225471
  Stats: 76 lines in 2 files changed: 8 ins; 10 del; 58 mod
  Patch: https://git.openjdk.org/jdk11u-dev/pull/2332.diff
  Fetch: git fetch https://git.openjdk.org/jdk11u-dev.git pull/2332/head:pull/2332

PR: https://git.openjdk.org/jdk11u-dev/pull/2332