RFR: 8198317: Enhance JavacTool.getTask for flexibility [v3]

[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.

Guoxiong Li has updated the pull request incrementally with one additional commit since the last revision:

  Revise test.

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

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/1896/files
  - new: https://git.openjdk.java.net/jdk/pull/1896/files/f73c4052..e13c072b

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=1896&range=02
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=1896&range=01-02

  Stats: 63 lines in 1 file changed: 52 ins; 0 del; 11 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