RFR: 8290313: Produce warning when user specified java.io.tmpdir directory doesn't exist [v2]

[Weibing Xiao]

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

Weibing Xiao has updated the pull request incrementally with one additional commit since the last revision:

  add the change for nio and update the code according to the comments

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/9989/files
  - new: https://git.openjdk.org/jdk/pull/9989/files/9f5a2983..cacf41d6

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=9989&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=9989&range=00-01

  Stats: 90 lines in 6 files changed: 69 ins; 12 del; 9 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