[crac] RFR: Reseed secure random on checkpoint restore [v8]

[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 with a new target base due to a merge or a rebase. The pull request now contains ten commits:

 - Merge branch 'crac' into SecureRandom
 - Exclude CheckpointException from import
 - Revert CheckpointException changes
 - Added assert in SecureRandom.invalidate()
 - Update object lock during checkpoint/restore
 - Set JDKResource priorities for SecureRandom
 - Merge branch 'crac' of https://github.com/openjdk/crac into SecureRandom
 - Add separate JDKResorce for seeder
 - Reseed secure random on checkpoint restore

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Changes: https://git.openjdk.java.net/crac/pull/7/files
 Webrev: https://webrevs.openjdk.java.net/?repo=crac&pr=7&range=07
  Stats: 258 lines in 4 files changed: 209 ins; 5 del; 44 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