RFR: 8254196: jshell infinite loops when startup script contains System.exit call

[Jan Lahoda]

If the startup script contains `System.exit(0);`, JShell will end up in an infinite loop of remote agent crashing, restarting, startup script running on the new instance, crashing, etc.

The proposal here is to avoid re-running the script from the beginning after the remote stops during startup. This should be fairly consistent with behavior of options like "/reload". Behavior in other cases should be unmodified.

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Commit messages:
 - 8254196: jshell infinite loops when startup script contains System.exit call

Changes: https://git.openjdk.java.net/jdk/pull/3150/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=3150&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8254196
  Stats: 27 lines in 3 files changed: 24 ins; 0 del; 3 mod
  Patch: https://git.openjdk.java.net/jdk/pull/3150.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/3150/head:pull/3150

PR: https://git.openjdk.java.net/jdk/pull/3150