[crac] RFR: Reseed NativePRNG on checkpoint restore [v2]

[Alexey Bakhtin]

> NativePRNG should be re-seeded during checkpoint/restore because it uses SHA1PRNG secure random for additional seed. It is seeded at initialization, so it is not re-seeded automatically during checkpoint/restore
> Also, the internal buffer should be cleared at the checkpoint.

Alexey Bakhtin has updated the pull request incrementally with one additional commit since the last revision:

  Use ReentrantReadWriteLock

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Changes:
  - all: https://git.openjdk.java.net/crac/pull/9/files
  - new: https://git.openjdk.java.net/crac/pull/9/files/894576ee..196edc75

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=crac&pr=9&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=crac&pr=9&range=00-01

  Stats: 13 lines in 2 files changed: 1 ins; 2 del; 10 mod
  Patch: https://git.openjdk.java.net/crac/pull/9.diff
  Fetch: git fetch https://git.openjdk.java.net/crac pull/9/head:pull/9

PR: https://git.openjdk.java.net/crac/pull/9