[crac] RFR: Reseed secure random on checkpoint restore [v5]

[Alexey Bakhtin]

> Proposed changes in the SecureRandom implementation allow invalidating and reseeding SHA1PRNG secure random during checkpoint/restore. SHA1PRNG can be invalidated and reseeded in case of being created with a default embedded seed generator. Also, SHA1PRNG is used as an additional seed generator to the SUN NativePRNG implementation, so it is desirable to have reseeded SHA1PRNG after restore.
> Two jtreg tests added: 
> - verify if no deadlocks introduced by checkpoint/restore
> - verify if SHA1PRNG is reseeded if created with default embedded seed generator

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

  Added assert in SecureRandom.invalidate()

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Changes:
  - all: https://git.openjdk.java.net/crac/pull/7/files
  - new: https://git.openjdk.java.net/crac/pull/7/files/3ade9580..8e7944f9

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=crac&pr=7&range=04
 - incr: https://webrevs.openjdk.java.net/?repo=crac&pr=7&range=03-04

  Stats: 2 lines in 1 file changed: 1 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/crac/pull/7.diff
  Fetch: git fetch https://git.openjdk.java.net/crac pull/7/head:pull/7

PR: https://git.openjdk.java.net/crac/pull/7