RFR: 7904083: Print fatal error messages to stderr

[SendaoYan]

Hi all,

Currently the fatal error message was print to stderr, shows as below. I think it's bettor to print the fatal error message to stderr.

The `>&2` usage for echo both works on linux and cygwin. I do not have other OS system to verify this change, but I think the risk of this change is low.

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

Commit messages:
 - 7904083: Print fatal error messages to stderr

Changes: https://git.openjdk.org/jtreg/pull/290/files
  Webrev: https://webrevs.openjdk.org/?repo=jtreg&pr=290&range=00
  Issue: https://bugs.openjdk.org/browse/CODETOOLS-7904083
  Stats: 10 lines in 1 file changed: 1 ins; 0 del; 9 mod
  Patch: https://git.openjdk.org/jtreg/pull/290.diff
  Fetch: git fetch https://git.openjdk.org/jtreg.git pull/290/head:pull/290

PR: https://git.openjdk.org/jtreg/pull/290