RFR: 8198317: Enhance JavacTool.getTask for flexibility

[Guoxiong Li]

Hi all,

This little patch enhances the setting of `Log` in `JavacTool.getTask`.

Thank you for taking the time to review.

Best Regards.

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

Commit messages:
 - 8198317: Enhance JavacTool.getTask for flexibility

Changes: https://git.openjdk.java.net/jdk/pull/1896/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=1896&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8198317
  Stats: 8 lines in 1 file changed: 6 ins; 0 del; 2 mod
  Patch: https://git.openjdk.java.net/jdk/pull/1896.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/1896/head:pull/1896

PR: https://git.openjdk.java.net/jdk/pull/1896