RFR: 8294402: Add diagnostic logging to VMProps.checkDockerSupport [v7]

[Mikhailo Seledtsov]

> Add log() and logToFile() methods to VMProps for diagnostic purposes.

Mikhailo Seledtsov has updated the pull request incrementally with one additional commit since the last revision:

  Re-added conditional logging per review discussion

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/12239/files
  - new: https://git.openjdk.org/jdk/pull/12239/files/1eef0f6f..b85636da

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=12239&range=06
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=12239&range=05-06

  Stats: 7 lines in 1 file changed: 7 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/12239.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/12239/head:pull/12239

PR: https://git.openjdk.org/jdk/pull/12239