RFR: 8290313: Produce warning when user specified java.io.tmpdir directory doesn't exist [v4]

[Weibing Xiao]

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

Weibing Xiao has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains 11 commits:

 - Merge branch 'master' into improve-directory-not-existing-error-message
 - new approach: print warning in StaticProperty.java
 - Merge branch 'master' into improve-directory-not-existing-error-message
 - add the change for nio and update the code according to the comments
 - 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
 - ... and 1 more: https://git.openjdk.org/jdk/compare/8487c56f...2da71bdc

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Changes: https://git.openjdk.org/jdk/pull/9989/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=9989&range=03
  Stats: 160 lines in 7 files changed: 147 ins; 2 del; 11 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