RFR: 8304498: JShell does not switch to raw mode when there is no /bin/test

[Jan Lahoda]

If JShell is run on a system that does not have `/bin/test` (which is, apparently, possible for some systems, which only have `/usr/bin/test`), it won't switch the terminal into the raw mode, and the input will not work properly.

The proposed fix herein is to detect whether `test` existing in `/usr/bin/test`, and if yes, use that location. Use the existing `/bin/test` otherwise.

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Commit messages:
 - 8304498: JShell does not switch to raw mode when there is no /bin/test

Changes: https://git.openjdk.org/jdk/pull/13100/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=13100&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8304498
  Stats: 63 lines in 2 files changed: 62 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/13100.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/13100/head:pull/13100

PR: https://git.openjdk.org/jdk/pull/13100