RFR: 8248381: Create a daemon thread for MonocleTimer

[John Neffenger]

Fixes [JDK-8248381](https://bugs.openjdk.java.net/browse/JDK-8248381).

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Commit messages:
 - 8248381: Create a daemon thread for MonocleTimer

Changes: https://git.openjdk.java.net/jfx/pull/256/files
 Webrev: https://webrevs.openjdk.java.net/jfx/256/webrev.00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8248381
  Stats: 8 lines in 1 file changed: 7 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/jfx/pull/256.diff
  Fetch: git fetch https://git.openjdk.java.net/jfx pull/256/head:pull/256

PR: https://git.openjdk.java.net/jfx/pull/256