RFR: 8267952: async logging supports to dynamically change tags and decorators

[Xin Liu]

Support dynamic reconfiguration for async logging. 2 unittests are provided.
The regression test discovers a race condition in LogTagSet::log() even with
synchronous logging. It's not MT-safe if context switch happens between the
creation of LogDecorations  and LogOutputList::Iterator. fixed.

-------------

Commit messages:
 - 8267952: async logging supports to dynamically change tags and decorators

Changes: https://git.openjdk.java.net/jdk/pull/4408/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=4408&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8267952
  Stats: 149 lines in 8 files changed: 139 ins; 5 del; 5 mod
  Patch: https://git.openjdk.java.net/jdk/pull/4408.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/4408/head:pull/4408

PR: https://git.openjdk.java.net/jdk/pull/4408