RFR: CODETOOLS-7902910: jcstress: Avoid creating lots of temporary files

[Aleksey Shipilev]

jcstress puts stdin and stdout into separate temporary files. It makes little sense, as the host VM would read those files into memory anyway. We can just buffer those to memory.

Additionally, we can stop creating compiler directives file when it is not needed.
Options

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Commit messages:
 - Use in-memory collectors

Changes: https://git.openjdk.java.net/jcstress/pull/41/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jcstress&pr=41&range=00
  Issue: https://bugs.openjdk.java.net/browse/CODETOOLS-7902910
  Stats: 118 lines in 2 files changed: 80 ins; 28 del; 10 mod
  Patch: https://git.openjdk.java.net/jcstress/pull/41.diff
  Fetch: git fetch https://git.openjdk.java.net/jcstress pull/41/head:pull/41

PR: https://git.openjdk.java.net/jcstress/pull/41