RFR: CODETOOLS-7902943: jcstress: Update console UX again

[Aleksey Shipilev]

We can make the console UX even better: print JVM/CPU in use counts, print sample frequencies, etc.

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Commit messages:
 - Cleanups
 - Print "<0.1%" where possible
 - More updates
 - More UX updates

Changes: https://git.openjdk.java.net/jcstress/pull/53/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jcstress&pr=53&range=00
  Issue: https://bugs.openjdk.java.net/browse/CODETOOLS-7902943
  Stats: 136 lines in 10 files changed: 92 ins; 8 del; 36 mod
  Patch: https://git.openjdk.java.net/jcstress/pull/53.diff
  Fetch: git fetch https://git.openjdk.java.net/jcstress pull/53/head:pull/53

PR: https://git.openjdk.java.net/jcstress/pull/53