RFR: 8198317: Enhance JavacTool.getTask for flexibility [v2]

[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:

  Add a test case.

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Changes:
  - all: https://git.openjdk.java.net/jdk/pull/1896/files
  - new: https://git.openjdk.java.net/jdk/pull/1896/files/5ac98f79..f73c4052

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=1896&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=1896&range=00-01

  Stats: 74 lines in 1 file changed: 74 ins; 0 del; 0 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