[crac] RFR: Linux file system watcher support [v3]

[joeylee]

> inotify monitors changes on filesystem, this support automatic restore for LinuxFileWatcher.
> 
> FileWatcherAfterRestoreTest verifies watcher service works after restore.
> FileWatcherTest verifies automatic closing inotiify fd
> 
> The watcher keys are still managed by user, so exception will be thrown if no watcher keys are leaked, as in FileWatcherWithOpenKeysTest

joeylee has updated the pull request incrementally with two additional commits since the last revision:

 - update test
 - update test

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

Changes:
  - all: https://git.openjdk.org/crac/pull/72/files
  - new: https://git.openjdk.org/crac/pull/72/files/36dfd224..40191d9b

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=crac&pr=72&range=02
 - incr: https://webrevs.openjdk.org/?repo=crac&pr=72&range=01-02

  Stats: 35 lines in 1 file changed: 25 ins; 1 del; 9 mod
  Patch: https://git.openjdk.org/crac/pull/72.diff
  Fetch: git fetch https://git.openjdk.org/crac.git pull/72/head:pull/72

PR: https://git.openjdk.org/crac/pull/72