[crac] RFR: Add CRAC_CRIU_LEAVE_RUNNING option

[Anton Kozlov]

The patch adds an option to the CRaC-CRIU glue code to continue running the original instance after the checkpoint. The central part is adding the right option to the CRIU command line. But after the checkpoint is done by CRIU, it's also necessary to communicate to the JVM that it can continue.

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Commit messages:
 - Process leave_running before buffer overflow possible
 - Add CRAC_CRIU_LEAVE_RUNNING option

Changes: https://git.openjdk.org/crac/pull/32/files
 Webrev: https://webrevs.openjdk.org/?repo=crac&pr=32&range=00
  Stats: 79 lines in 2 files changed: 79 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/crac/pull/32.diff
  Fetch: git fetch https://git.openjdk.org/crac pull/32/head:pull/32

PR: https://git.openjdk.org/crac/pull/32