RFR: 8294402: Add diagnostic logging to VMProps.checkDockerSupport [v4]

[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:

  Review feedback: printing stdout and stderr files to log()

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Changes:
  - all: https://git.openjdk.org/jdk/pull/12239/files
  - new: https://git.openjdk.org/jdk/pull/12239/files/02d6833a..b1aa1c4b

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=12239&range=03
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=12239&range=02-03

  Stats: 33 lines in 1 file changed: 29 ins; 0 del; 4 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