RFR: Use timed wait to sleep control thread

[earthling-amzn]

Using a timed `wait` rather than a naked sleep allows the control thread to be more responsive to requests from mutators and the regulator thread to start GC cycles. The sleep time is also changed from `ShenandoahControlIntervalMin` to `ShenandoahControlIntervalMax` to reduce unnecessary polling cycles. We could use a plain `wait`, but the control thread is responsible for periodically sending allocation metrics to the `pacer`.

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Commit messages:
 - Use timed wait to sleep control thread

Changes: https://git.openjdk.java.net/shenandoah/pull/28/files
 Webrev: https://webrevs.openjdk.java.net/?repo=shenandoah&pr=28&range=00
  Stats: 17 lines in 2 files changed: 12 ins; 0 del; 5 mod
  Patch: https://git.openjdk.java.net/shenandoah/pull/28.diff
  Fetch: git fetch https://git.openjdk.java.net/shenandoah pull/28/head:pull/28

PR: https://git.openjdk.java.net/shenandoah/pull/28