[crac] RFR: Get tracing properties lazily

[Anton Kozlov]

A minor change to make tracing flags lazily initialized.

Without this, reading j.l.System's properties during jdk.crac.Core initialization could lead to NPE if happens too early, i.e. before j.l.System's properties are initialized.

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Commit messages:
 - Get tracing properties lazily

Changes: https://git.openjdk.java.net/crac/pull/12/files
 Webrev: https://webrevs.openjdk.java.net/?repo=crac&pr=12&range=00
  Stats: 86 lines in 3 files changed: 60 ins; 16 del; 10 mod
  Patch: https://git.openjdk.java.net/crac/pull/12.diff
  Fetch: git fetch https://git.openjdk.java.net/crac pull/12/head:pull/12

PR: https://git.openjdk.java.net/crac/pull/12