RFR: 8290313: Produce warning when user specified java.io.tmpdir directory doesn't exist

[Weibing Xiao]

8290313: Produce warning when user specified java.io.tmpdir directory doesn't exist

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Commit messages:
 - new approach
 - change based on the review
 - updating according to the comments
 - Merge branch 'master' of https://github.com/openjdk/jdk into improve-directory-not-existing-error-message
 - update error message
 - error message for non-existing directory
 - improve error message when file directory does not exist

Changes: https://git.openjdk.org/jdk/pull/9989/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=9989&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8290313
  Stats: 82 lines in 3 files changed: 79 ins; 0 del; 3 mod
  Patch: https://git.openjdk.org/jdk/pull/9989.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/9989/head:pull/9989

PR: https://git.openjdk.org/jdk/pull/9989